Thursday
Biosensor reveals multiple sources for mitochondrial NAD⁺
Monday
Coenzyme A: when small is mighty
By Robert Leonardi and Suzanne Jackowski
Coenzyme A is an essential, universally distributed, thiol-containing cofactor that works as the major acyl group carrier in all cells. This molecule is involved in hundreds of reactions and is required for the metabolism of fatty acids, carbohydrates, amino acids and ketone bodies.
CoA is a major regulator of energy metabolism, although it often is overlooked. Acetyl-CoA in particular is strategically positioned at the crossroads of energy metabolism. Just like all the roads lead to Rome, both anabolic and catabolic pathways converge at the formation of this small molecule, yet acetyl-CoA maintains order by reinforcing the partition of pyruvate between synthesis and degradation through its differential regulation of pyruvate dehydrogenase and carboxylase. Traffic control beyond this metabolic junction is exerted by acetyl- and other acyl-CoAs through both allosteric and post-translational regulation.
Several acyl-CoAs produced as metabolic intermediates are potent allosteric modulators of key enzymes, such as carnitine palmitoyltransferase I and acetyl-CoA carboxylase, and transcription factors, such as HNF4-α (1) and PPARα (2). Acetyl-CoA is used to modify enzymes, transcription factors and chromatin covalently and reversibly to govern their activities (3, 4, 5). Covalent acylation by long-chain acyl-CoAs directs proteins to membranes where substrates are activated and stimulate cell growth and proliferation in cancer (6).
These ingenious mechanisms coordinate the expression and activity of a multitude of enzymes and processes with the energy state of the cell. Thus, CoA and a few other small molecules like NAD+ and ATP can act as global regulators of cellular metabolism both together with and independent from the action of key transcription factors.
Consistent with these key functions, CoA levels are flexible in cells so that the available supply is sufficiently adaptive to metabolic challenge. But at the same time, CoA levels are maintained at threshold amounts, suggesting that an oversupply could be detrimental to function. Decades of studies have established that regulation of the CoA biosynthetic pathway occurs at the initial step catalyzed by pantothenate kinase (PanK) in bacteria and eukaryotes (7, 8).
Mammals possess four closely related PanK isoforms, PanK1α, 1β, 2 and 3, and these enzymes are regulated through feedback inhibition by CoA species and through activation by long-chain acylcarnitines and acylethanolamides. Not all the PanK isoforms are equally responsive to this allosteric regulation, and PanK2 and 3 are significantly more sensitive than PanK1α and 1β. The localization of the PanK isoforms in different subcellular compartments and their tissue-selective distribution profiles are additional features that provide combinatorial control over CoA levels in distinct cell types.
But why is there so much redundancy, and why are there so many variations on the same theme? We recently have started to get some answers from the generation of mice that lack one or more PanKs.
The single Pank1, Pank2 and Pank3 knockout mice are viable and overtly normal, with the exception of the Pank1 knockout mice that exhibit a clear metabolic phenotype. Deletion of any two Pank genes leads to either embryonic lethality (Pank1/3 and Pank2/3) or death before weaning age (Pank1/2), indicating that the isoforms can compensate for each other and that redundancy is necessary for life. The combination of isoform abundance and regulatory properties roughly correlates with the total amount of CoA in tissues and organs, so that tissues where PanK1α or 1β are most abundant (liver, heart, kidney) have higher CoA levels than tissues where PanK2 or 3 predominate (brain, skeletal muscle).
Finally, the particular localization of each PanK isoform in the cytosol, mitochondrion or nucleus may enable the response to ligands that govern activity and flux through the CoA biosynthetic pathway. The PanKs may be sensors in situ that respond to fluctuations in the local concentration of acetyl-CoA, acyl-carnitine or acylethanolamide and adjust the rate of CoA biosynthesis.
The recent characterization of mice with complete chemical inhibition of all the PanKs (9) and of mice lacking Pank1 alone or in combination with Pank2 (10, 11) has established clearly the connection between PanK expression → CoA levels → metabolism. This represents an important starting point to try and understand the complex pathology of PKAN (pantothenate kinase-associated neurodegeneration), a severe neurological disorder caused by mutations in the human PANK2 gene. The majority of these mutations are expected to decrease significantly or abolish PanK2 activity, thus suggesting that lower CoA could be the underlying cause of reduced neuronal metabolism and function in PKAN patients.
Unfortunately, Pank2 knockout mice do not reproduce the human disease, and an important future challenge will be to generate a mouse model to investigate the connection between CoA levels and neurodegeneration and, above all, to accelerate the identification of a treatment for the disease.
Given the central role of CoA in the regulation of metabolism, another important question to address will be whether metabolic diseases like diabetes are associated with dysregulated tissue CoA levels and what the importance of CoA-degrading enzymes is in the regulation of this cofactor. Clearly, research thus far has shown that cofactors such as CoA, ATP and NAD+ can limit the output of a pathway in a manner similar to reduced enzyme levels.
Perhaps CoA is regulated to prevent overactivity within a pathway, and the future research challenge will be to establish the hierarchy among those biological processes that require CoA. CoA is required for hundreds of reactions and regulates metabolism at several different levels that include 1) substrate delivery for enzymatic reactions, 2) allosteric and post-translational regulation of enzymatic activity, and 3) regulation of gene expression through reversible acetylation of histones and transcription factors.
So keep CoA in mind next time you see a metabolic phenotype: It might just happen that a pharmacological organic acid is activated by this cofactor, thereby reducing the effective concentration of CoA for normal cellular and biochemical functions. © Copyright American Society
Coenzyme A is an essential, universally distributed, thiol-containing cofactor that works as the major acyl group carrier in all cells. This molecule is involved in hundreds of reactions and is required for the metabolism of fatty acids, carbohydrates, amino acids and ketone bodies.
CoA is a major regulator of energy metabolism, although it often is overlooked. Acetyl-CoA in particular is strategically positioned at the crossroads of energy metabolism. Just like all the roads lead to Rome, both anabolic and catabolic pathways converge at the formation of this small molecule, yet acetyl-CoA maintains order by reinforcing the partition of pyruvate between synthesis and degradation through its differential regulation of pyruvate dehydrogenase and carboxylase. Traffic control beyond this metabolic junction is exerted by acetyl- and other acyl-CoAs through both allosteric and post-translational regulation.
Several acyl-CoAs produced as metabolic intermediates are potent allosteric modulators of key enzymes, such as carnitine palmitoyltransferase I and acetyl-CoA carboxylase, and transcription factors, such as HNF4-α (1) and PPARα (2). Acetyl-CoA is used to modify enzymes, transcription factors and chromatin covalently and reversibly to govern their activities (3, 4, 5). Covalent acylation by long-chain acyl-CoAs directs proteins to membranes where substrates are activated and stimulate cell growth and proliferation in cancer (6).
These ingenious mechanisms coordinate the expression and activity of a multitude of enzymes and processes with the energy state of the cell. Thus, CoA and a few other small molecules like NAD+ and ATP can act as global regulators of cellular metabolism both together with and independent from the action of key transcription factors.
Consistent with these key functions, CoA levels are flexible in cells so that the available supply is sufficiently adaptive to metabolic challenge. But at the same time, CoA levels are maintained at threshold amounts, suggesting that an oversupply could be detrimental to function. Decades of studies have established that regulation of the CoA biosynthetic pathway occurs at the initial step catalyzed by pantothenate kinase (PanK) in bacteria and eukaryotes (7, 8).
Mammals possess four closely related PanK isoforms, PanK1α, 1β, 2 and 3, and these enzymes are regulated through feedback inhibition by CoA species and through activation by long-chain acylcarnitines and acylethanolamides. Not all the PanK isoforms are equally responsive to this allosteric regulation, and PanK2 and 3 are significantly more sensitive than PanK1α and 1β. The localization of the PanK isoforms in different subcellular compartments and their tissue-selective distribution profiles are additional features that provide combinatorial control over CoA levels in distinct cell types.
But why is there so much redundancy, and why are there so many variations on the same theme? We recently have started to get some answers from the generation of mice that lack one or more PanKs.
The single Pank1, Pank2 and Pank3 knockout mice are viable and overtly normal, with the exception of the Pank1 knockout mice that exhibit a clear metabolic phenotype. Deletion of any two Pank genes leads to either embryonic lethality (Pank1/3 and Pank2/3) or death before weaning age (Pank1/2), indicating that the isoforms can compensate for each other and that redundancy is necessary for life. The combination of isoform abundance and regulatory properties roughly correlates with the total amount of CoA in tissues and organs, so that tissues where PanK1α or 1β are most abundant (liver, heart, kidney) have higher CoA levels than tissues where PanK2 or 3 predominate (brain, skeletal muscle).
Finally, the particular localization of each PanK isoform in the cytosol, mitochondrion or nucleus may enable the response to ligands that govern activity and flux through the CoA biosynthetic pathway. The PanKs may be sensors in situ that respond to fluctuations in the local concentration of acetyl-CoA, acyl-carnitine or acylethanolamide and adjust the rate of CoA biosynthesis.
The recent characterization of mice with complete chemical inhibition of all the PanKs (9) and of mice lacking Pank1 alone or in combination with Pank2 (10, 11) has established clearly the connection between PanK expression → CoA levels → metabolism. This represents an important starting point to try and understand the complex pathology of PKAN (pantothenate kinase-associated neurodegeneration), a severe neurological disorder caused by mutations in the human PANK2 gene. The majority of these mutations are expected to decrease significantly or abolish PanK2 activity, thus suggesting that lower CoA could be the underlying cause of reduced neuronal metabolism and function in PKAN patients.
Unfortunately, Pank2 knockout mice do not reproduce the human disease, and an important future challenge will be to generate a mouse model to investigate the connection between CoA levels and neurodegeneration and, above all, to accelerate the identification of a treatment for the disease.
Given the central role of CoA in the regulation of metabolism, another important question to address will be whether metabolic diseases like diabetes are associated with dysregulated tissue CoA levels and what the importance of CoA-degrading enzymes is in the regulation of this cofactor. Clearly, research thus far has shown that cofactors such as CoA, ATP and NAD+ can limit the output of a pathway in a manner similar to reduced enzyme levels.
Perhaps CoA is regulated to prevent overactivity within a pathway, and the future research challenge will be to establish the hierarchy among those biological processes that require CoA. CoA is required for hundreds of reactions and regulates metabolism at several different levels that include 1) substrate delivery for enzymatic reactions, 2) allosteric and post-translational regulation of enzymatic activity, and 3) regulation of gene expression through reversible acetylation of histones and transcription factors.
So keep CoA in mind next time you see a metabolic phenotype: It might just happen that a pharmacological organic acid is activated by this cofactor, thereby reducing the effective concentration of CoA for normal cellular and biochemical functions. © Copyright American Society
REFERENCES
- 1. ↵ Bogan, A.A. et al. J. Mol. Biol. 302, 831 – 851 (2000).
- 2. ↵ Schroeder, F. et al. Lipids 40, 559 – 568 (2005).
- 3. ↵ Cai, L. et al. Mol. Cell 42, 426 – 437 (2011).
- 4. ↵ Lundby, A. et al. Cell Rep. 2, 419 – 431 (2012).
- 5. ↵ Siudeja, K. et al. EMBO Mol. Med. 3, 755 – 766 (2011).
- 6. ↵ Triola, G. et al. ACS Chem. Biol. 7, 87 – 99 (2012).
- 7. ↵ Rock, C.O. et al. J. Biol. Chem. 275, 1377 – 1383 (2000).
- 8. ↵ Vallari, D. S. et al. J. Biol. Chem. 262, 2468 – 2471 (1987).
- 9. ↵ Zhang, Y.M. et al. Chem. Biol. 14, 291 – 302 (2007).
- 10. ↵ Garcia, M. et al. PLoS ONE 7, e40871 (2012).
- 11. ↵ Leonardi, R. et al. PLoS ONE 5, e11107 (2010).
Roberta Leonardi (roleonardi@hsc.wvu.edu) is a scientific laboratory manager in the Department of Infectious Diseases at St. Jude Children’s Research Hospital. Later this month, she will be an assistant professor at West Virginia University. Suzanne Jackowski (suzanne.jackowski@stjude.org) is a faculty member at St. Jude Children’s Research Hospital and executive editor of BBA-Molecular and Cell Biology of Lipids.
Thursday
What is a Coenzyme
What is a coenzyme. The Columbia Encyclopedia defines A coenzyme as any one group of relatively small organic molecules required for the catalytic function of certain enzymes. A coenzyme may either be attached by covalent bonds to a particular enzyme or exist freely in solution, but in either case it participates intimately in the chemical reactions catalyzed by the enzyme. Often a coenzyme is structurally altered in the course of these reactions, but it is always restored to its original form in subsequent reactions catalyzed by other enzyme systems.
Adenosine triphosphate (ATP) is a coenzyme of vast importance in the transfer of chemical energy derived from biochemical oxidations. Other nucleotides (formed from uracil, cytosine, guanine, and inosine) have also been found to act as coenzymes. For example, uridine triphosphate-a derivative of uracil-has been demonstrated to be of great importance in the metabolism of carbohydrates, as in the biosynthesis of glycogen and sucrose.
Those coenzymes that have been found to be necessary in the diet are vitamins. One such compound, biotin, is a member of the B complex; it was first isolated in 1935 from dried egg yolk, and its structure was established in 1942. Biotin is usually found attached to a lysine residue in certain enzymes, where it participates in reactions involving the transfer of carboxyl (−COOH) groups; one such reaction is essential for the synthesis of fatty acids.
Another group of coenzymes is the cobalamin family; one member, cyanocobalamin (vitamin B12) is known to be essential in the diet, although its role in metabolism remains obscure. Closely related cobalamins seem to be involved in the biosynthesis of methionine and methane. The complicated cyanocobalamin molecule was reported in 1973 to have been synthesized; it was first isolated from liver some 25 years prior to that date.
Coenzyme A has been shown to participate in a variety of biochemical reactions, all involving acyl groups such as the acetyl unit; it is, for instance, associated with the pivotal first step of the Krebs cycle, in which an acetyl unit (the breakdown product of carbohydrates) is introduced into the cycle to be converted eventually into carbon dioxide, water, and chemical energy. Coenzyme A is derived from adenine, ribose, and pantothenic acid (a vitamin of the B complex).
The two flavin coenzymes, riboflavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), occur universally in living organisms and play important roles in biochemical oxidations and reductions. They are usually found tightly bound to certain enzymes (flavoproteins) and are derived from riboflavin (vitamin B2).
Glutathione, a tripeptide consisting of residues of glutamic acid, cysteine, and glycine, is known to act as a coenzyme in a few enzymatic reactions, but its importance may lie in its role as a nonspecific reducing agent within the cell. It is hypothesized that glutathione serves to maintain the biological activity of certain proteins by keeping selected cysteine sidechains in the reduced thiol form, thereby not allowing these residues to oxidize and cross-link with one another to form cystine residues. (Unnecessary cross-links often result in distortions of protein structure.)
Heme, a complicated molecule containing iron in the ferrous state, serves as a coenzyme in a variety of biochemical processes. It forms an essential part of the structure of hemoglobin and participates intimately in the uptake and release of oxygen by this protein. (In this case the use of the word coenzyme may be inappropriate in that often hemoglobin is not considered to be an enzyme, since it does not catalyze a chemical reaction.) Heme is an important part of the cytochromes, enzymes that catalyze the biochemical oxidations and reductions involved in the production of chemical energy in the form of ATP; heme is also associated with the various enzymes that catalyze the cleavage of peroxides.
Lipoic acid seems to be involved in the removal of carboxyl groups from α-keto acids and in the transfer of the remaining acyl groups to various acceptors. Lipoic acid in fact transfers the acetyl group of pyruvic acid to coenzyme A. Like biotin, lipoic acid is commonly found attached to lysine residues within certain enzymes. It was first reported to have been purified and isolated in crystalline form in 1953.
The nicotinamide nucleotides were the first coenzymes to be detected (1904) in extracts of a living organism. Nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) are derived from adenine, ribose, and nicotinic acid or niacin (a vitamin of the B complex) and are important intermediates in the biochemical oxidations and reductions that provide chemical energy within the cell. Both NAD and NADP can be reduced by accepting a hydride ion (H−, a proton with two electrons) from an appropriate donor; the resulting NADH and NADPH can then be oxidized back to their original states by transferring their hydride ions to various acceptors. In this fashion electron pairs (and protons) are shuttled about in the cell from high-energy donors to lower-energy acceptors. As a general rule, NADPH donates its hydride ions to biosynthetic processes, such as the fixing of carbon dioxide to make carbohydrates during the dark reaction of photosynthesis. NADH, on the other hand, donates its hydride ions to systems such as the cytochromes, which eventually donate them to oxygen to make (with the addition of a proton) water, producing chemical energy in the form of ATP as a byproduct; the process is not yet completely understood.
Pyridoxal phosphate is a coenzyme that is essential for many enzymatic reactions, almost all of which are associated with amino acid metabolism. It is, for example, involved in the synthesis of tryptophan, a derivative of pyridoxine (another vitamin of the B complex).
The coenzyme tetrahydrofolic acid is derived in humans from the B-complex vitamin folic acid. This coenzyme and its close relatives participate in the transfer of various carbon fragments from one molecule to another; they are, for instance, involved in the synthesis of methionine and thymine.
Thiamine pyrophosphate is derived from another B-complex vitamin, thiamine. This coenzyme often plays a role in the removal of carboxyl (−COOH) groups from organic acids, releasing the carbon and oxygen atoms as carbon dioxide (CO2). This coenzyme, for example, helps to remove a carboxyl group from pyruvic acid, leaving behind an acetyl group, which it donates to lipoic acid; the lipoic acid then transfers the acetyl group to coenzyme A, which finally inserts it into the beginning of the Krebs cycle. This important three-step enzymatic process requires the participation of three coenzymes; hundreds of other biochemical reactions require coenzymes as well, and this serves to explain the great significance of those molecules in the functioning of living organisms. In the case of human beings, it also serves to explain the importance of proper dietary intake of vitamins, which provide the only source of certain "building blocks" for several of these coenzymes.
This is a direct reference from Columbia Encyclopedia.
Adenosine triphosphate (ATP) is a coenzyme of vast importance in the transfer of chemical energy derived from biochemical oxidations. Other nucleotides (formed from uracil, cytosine, guanine, and inosine) have also been found to act as coenzymes. For example, uridine triphosphate-a derivative of uracil-has been demonstrated to be of great importance in the metabolism of carbohydrates, as in the biosynthesis of glycogen and sucrose.
Those coenzymes that have been found to be necessary in the diet are vitamins. One such compound, biotin, is a member of the B complex; it was first isolated in 1935 from dried egg yolk, and its structure was established in 1942. Biotin is usually found attached to a lysine residue in certain enzymes, where it participates in reactions involving the transfer of carboxyl (−COOH) groups; one such reaction is essential for the synthesis of fatty acids.
Another group of coenzymes is the cobalamin family; one member, cyanocobalamin (vitamin B12) is known to be essential in the diet, although its role in metabolism remains obscure. Closely related cobalamins seem to be involved in the biosynthesis of methionine and methane. The complicated cyanocobalamin molecule was reported in 1973 to have been synthesized; it was first isolated from liver some 25 years prior to that date.
Coenzyme A has been shown to participate in a variety of biochemical reactions, all involving acyl groups such as the acetyl unit; it is, for instance, associated with the pivotal first step of the Krebs cycle, in which an acetyl unit (the breakdown product of carbohydrates) is introduced into the cycle to be converted eventually into carbon dioxide, water, and chemical energy. Coenzyme A is derived from adenine, ribose, and pantothenic acid (a vitamin of the B complex).
The two flavin coenzymes, riboflavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), occur universally in living organisms and play important roles in biochemical oxidations and reductions. They are usually found tightly bound to certain enzymes (flavoproteins) and are derived from riboflavin (vitamin B2).
Glutathione, a tripeptide consisting of residues of glutamic acid, cysteine, and glycine, is known to act as a coenzyme in a few enzymatic reactions, but its importance may lie in its role as a nonspecific reducing agent within the cell. It is hypothesized that glutathione serves to maintain the biological activity of certain proteins by keeping selected cysteine sidechains in the reduced thiol form, thereby not allowing these residues to oxidize and cross-link with one another to form cystine residues. (Unnecessary cross-links often result in distortions of protein structure.)
Heme, a complicated molecule containing iron in the ferrous state, serves as a coenzyme in a variety of biochemical processes. It forms an essential part of the structure of hemoglobin and participates intimately in the uptake and release of oxygen by this protein. (In this case the use of the word coenzyme may be inappropriate in that often hemoglobin is not considered to be an enzyme, since it does not catalyze a chemical reaction.) Heme is an important part of the cytochromes, enzymes that catalyze the biochemical oxidations and reductions involved in the production of chemical energy in the form of ATP; heme is also associated with the various enzymes that catalyze the cleavage of peroxides.
Lipoic acid seems to be involved in the removal of carboxyl groups from α-keto acids and in the transfer of the remaining acyl groups to various acceptors. Lipoic acid in fact transfers the acetyl group of pyruvic acid to coenzyme A. Like biotin, lipoic acid is commonly found attached to lysine residues within certain enzymes. It was first reported to have been purified and isolated in crystalline form in 1953.
The nicotinamide nucleotides were the first coenzymes to be detected (1904) in extracts of a living organism. Nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) are derived from adenine, ribose, and nicotinic acid or niacin (a vitamin of the B complex) and are important intermediates in the biochemical oxidations and reductions that provide chemical energy within the cell. Both NAD and NADP can be reduced by accepting a hydride ion (H−, a proton with two electrons) from an appropriate donor; the resulting NADH and NADPH can then be oxidized back to their original states by transferring their hydride ions to various acceptors. In this fashion electron pairs (and protons) are shuttled about in the cell from high-energy donors to lower-energy acceptors. As a general rule, NADPH donates its hydride ions to biosynthetic processes, such as the fixing of carbon dioxide to make carbohydrates during the dark reaction of photosynthesis. NADH, on the other hand, donates its hydride ions to systems such as the cytochromes, which eventually donate them to oxygen to make (with the addition of a proton) water, producing chemical energy in the form of ATP as a byproduct; the process is not yet completely understood.
Pyridoxal phosphate is a coenzyme that is essential for many enzymatic reactions, almost all of which are associated with amino acid metabolism. It is, for example, involved in the synthesis of tryptophan, a derivative of pyridoxine (another vitamin of the B complex).
The coenzyme tetrahydrofolic acid is derived in humans from the B-complex vitamin folic acid. This coenzyme and its close relatives participate in the transfer of various carbon fragments from one molecule to another; they are, for instance, involved in the synthesis of methionine and thymine.
Thiamine pyrophosphate is derived from another B-complex vitamin, thiamine. This coenzyme often plays a role in the removal of carboxyl (−COOH) groups from organic acids, releasing the carbon and oxygen atoms as carbon dioxide (CO2). This coenzyme, for example, helps to remove a carboxyl group from pyruvic acid, leaving behind an acetyl group, which it donates to lipoic acid; the lipoic acid then transfers the acetyl group to coenzyme A, which finally inserts it into the beginning of the Krebs cycle. This important three-step enzymatic process requires the participation of three coenzymes; hundreds of other biochemical reactions require coenzymes as well, and this serves to explain the great significance of those molecules in the functioning of living organisms. In the case of human beings, it also serves to explain the importance of proper dietary intake of vitamins, which provide the only source of certain "building blocks" for several of these coenzymes.
This is a direct reference from Columbia Encyclopedia.
Sunday
Comparative genomics of NAD(P) biosynthesis and novel antibiotic drug targets
Abstract
NAD(P) is an indispensable cofactor for all organisms and its biosynthetic pathways are proposed as promising novel antibiotics targets against pathogens such as Mycobacterium tuberculosis. Six NAD(P) biosynthetic pathways were reconstructed by comparative genomics: de novo pathway (Asp), de novo pathway (Try), NmR pathway I (RNK-dependent), NmR pathway II (RNK-independent), Niacin salvage, and Niacin recycling. Three enzymes pivotal to the key reactions of NAD(P) biosynthesis are shared by almost all organisms, that is, NMN/NaMN adenylyltransferase (NMN/NaMNAT), NAD synthetase (NADS), and NAD kinase (NADK). They might serve as ideal broad spectrum antibiotic targets. Studies in M. tuberculosis have in part tested such hypothesis. Three regulatory factors NadR, NiaR, and NrtR, which regulate NAD biosynthesis, have been identified. M. tuberculosis NAD(P) metabolism and regulation thereof, potential drug targets and drug development are summarized in this paper. J. Cell. Physiol. 226: 331–340, 2011.
NAD(P) is an indispensable cofactor for all organisms and its biosynthetic pathways are proposed as promising novel antibiotics targets against pathogens such as Mycobacterium tuberculosis. Six NAD(P) biosynthetic pathways were reconstructed by comparative genomics: de novo pathway (Asp), de novo pathway (Try), NmR pathway I (RNK-dependent), NmR pathway II (RNK-independent), Niacin salvage, and Niacin recycling. Three enzymes pivotal to the key reactions of NAD(P) biosynthesis are shared by almost all organisms, that is, NMN/NaMN adenylyltransferase (NMN/NaMNAT), NAD synthetase (NADS), and NAD kinase (NADK). They might serve as ideal broad spectrum antibiotic targets. Studies in M. tuberculosis have in part tested such hypothesis. Three regulatory factors NadR, NiaR, and NrtR, which regulate NAD biosynthesis, have been identified. M. tuberculosis NAD(P) metabolism and regulation thereof, potential drug targets and drug development are summarized in this paper. J. Cell. Physiol. 226: 331–340, 2011.
Wednesday
What Is Coenzyme A or Acetyl-CoA
Acetyl coenzyme A or Acetyl-CoA is an important molecule in metabolism, used in many biochemical reactions. Its main function is to convey the carbon atoms within the acetyl group to the citric acid cycle to be oxidized for energy production. In chemical structure, acetyl-CoA is the thioester between coenzyme A (a thiol) and acetic acid (an acyl group carrier). Acetyl-CoA is produced during the second step of aerobic cellular respiration, pyruvate decarboxylation, which occurs in the matrix of the mitochondria. Acetyl-CoA then enters the citric acid cycle.
Acetyl-CoA is also an important component in the biogenic synthesis of the neurotransmitter acetylcholine. Choline, in combination with Acetyl-CoA, is catalyzed by the enzyme choline acetyltransferase to produce acetylcholine and a coenzyme a byproduct.
Pyruvate dehydrogenase and pyruvate formate lyase reactions
The oxidative conversion of pyruvate into acetyl-CoA is referred to as the pyruvate dehydrogenase reaction. It is catalyzed by the pyruvate dehydrogenase complex. Other conversions between pyruvate and acetyl-CoA are possible. For example, pyruvate formate lyase disproportionates pyruvate into acetyl-CoA and formic acid. The pyruvate formate lyase reaction does not involve any net oxidation or reduction.
Fatty acid metabolism
In animals, acetyl-CoA is essential to the balance between carbohydrate metabolism and fat metabolism (see fatty acid synthesis). In normal circumstances, acetyl-CoA from fatty acid metabolism feeds into the citric acid cycle, contributing to the cell's energy supply. In the liver, when levels of circulating fatty acids are high, the production of acetyl-CoA from fat breakdown exceeds the cellular energy requirements. To make use of the energy available from the excess acetyl-CoA, ketone bodies are produced which can then circulate in the blood. Therefore, when at rest, both the skeletal and cardiac muscles satisfy their energy requirement mainly through oxidation of ketone bodies.[citation needed]
In some circumstances, this can lead to the presence of very high levels of ketone bodies in the blood, a condition called ketosis. Benign dietary ketosis can safely occur in people following low-carbohydrate diets, which cause fats to be metabolised as a major source of energy. This is different from ketosis brought on as a result of starvation, and from ketoacidosis, a dangerous condition that can affect diabetics.
In plants, de novo fatty acid synthesis occurs in the plastids. Many seeds accumulate large reservoirs of seed oils to support germination and early growth of the seedling before it is a net photosynthetic organism. Fatty acids are incorporated into membrane lipids, the major component of most membranes.
Other reactions
Two acetyl-CoA can be condensed to create acetoacetyl-CoA, the first step in the HMG-CoA/ mevalonic acid pathway leading to synthesis of isoprenoids. In animals HMG-CoA is a vital precursor to cholesterol and ketone synthesis.
Acetyl-CoA is also the source of the acetyl group incorporated onto certain lysine residues of histone and non-histone proteins in the post-translational modification acetylation, a reaction catalyzed by acetyltransferases.
In plants and animals, cytosolic acetyl-CoA is synthesized by ATP citrate lyase [1]. When glucose is abundant in the blood of animals, it is converted via glycolysis in the cytosol to pyruvate, and thence to acetyl-CoA in the mitochondrion. The excess of acetyl-CoA results in production of excess citrate, which is exported into the cytosol to give rise to cytosolic acetyl-CoA.
Acetyl-CoA can be carboxylated in the cytosol by acetyl-CoA carboxylase, giving rise to malonyl-CoA, a substrate required for synthesis of flavonoids and related polyketides, for elongation of fatty acids to produce waxes, cuticle, and seed oils in members of the Brassica family, and for malonation of proteins and other phytochemicals [2].
In plants, these include sesquiterpenes, brassinosteroids (hormones), and membrane sterols.
Acetyl-CoA is also an important component in the biogenic synthesis of the neurotransmitter acetylcholine. Choline, in combination with Acetyl-CoA, is catalyzed by the enzyme choline acetyltransferase to produce acetylcholine and a coenzyme a byproduct.
Pyruvate dehydrogenase and pyruvate formate lyase reactions
The oxidative conversion of pyruvate into acetyl-CoA is referred to as the pyruvate dehydrogenase reaction. It is catalyzed by the pyruvate dehydrogenase complex. Other conversions between pyruvate and acetyl-CoA are possible. For example, pyruvate formate lyase disproportionates pyruvate into acetyl-CoA and formic acid. The pyruvate formate lyase reaction does not involve any net oxidation or reduction.
Fatty acid metabolism
In animals, acetyl-CoA is essential to the balance between carbohydrate metabolism and fat metabolism (see fatty acid synthesis). In normal circumstances, acetyl-CoA from fatty acid metabolism feeds into the citric acid cycle, contributing to the cell's energy supply. In the liver, when levels of circulating fatty acids are high, the production of acetyl-CoA from fat breakdown exceeds the cellular energy requirements. To make use of the energy available from the excess acetyl-CoA, ketone bodies are produced which can then circulate in the blood. Therefore, when at rest, both the skeletal and cardiac muscles satisfy their energy requirement mainly through oxidation of ketone bodies.[citation needed]
In some circumstances, this can lead to the presence of very high levels of ketone bodies in the blood, a condition called ketosis. Benign dietary ketosis can safely occur in people following low-carbohydrate diets, which cause fats to be metabolised as a major source of energy. This is different from ketosis brought on as a result of starvation, and from ketoacidosis, a dangerous condition that can affect diabetics.
In plants, de novo fatty acid synthesis occurs in the plastids. Many seeds accumulate large reservoirs of seed oils to support germination and early growth of the seedling before it is a net photosynthetic organism. Fatty acids are incorporated into membrane lipids, the major component of most membranes.
Other reactions
Two acetyl-CoA can be condensed to create acetoacetyl-CoA, the first step in the HMG-CoA/ mevalonic acid pathway leading to synthesis of isoprenoids. In animals HMG-CoA is a vital precursor to cholesterol and ketone synthesis.
Acetyl-CoA is also the source of the acetyl group incorporated onto certain lysine residues of histone and non-histone proteins in the post-translational modification acetylation, a reaction catalyzed by acetyltransferases.
In plants and animals, cytosolic acetyl-CoA is synthesized by ATP citrate lyase [1]. When glucose is abundant in the blood of animals, it is converted via glycolysis in the cytosol to pyruvate, and thence to acetyl-CoA in the mitochondrion. The excess of acetyl-CoA results in production of excess citrate, which is exported into the cytosol to give rise to cytosolic acetyl-CoA.
Acetyl-CoA can be carboxylated in the cytosol by acetyl-CoA carboxylase, giving rise to malonyl-CoA, a substrate required for synthesis of flavonoids and related polyketides, for elongation of fatty acids to produce waxes, cuticle, and seed oils in members of the Brassica family, and for malonation of proteins and other phytochemicals [2].
In plants, these include sesquiterpenes, brassinosteroids (hormones), and membrane sterols.
Thursday
Preparation, characterization and in silico modeling of biodegradable nanoparticles containing cyclosporine A and coenzyme Q10
Abstract. Combination therapy will soon become a reality, particularly for those patients requiring poly-therapy to treat co-existing disease states. This becomes all the more important with the increasing cost, time and complexity of the drug discovery process prompting one to look at new delivery systems to increase the efficacy, safety and patient compliance of existing drugs.
Along this line, we attempted to design nano-scale systems for simultaneous encapsulation of cyclosporine A (CsA) and coenzyme Q10 (CoQ10) and model their encapsulation and release kinetics. The in vitro characterization of the co-encapsulated nanoparticles revealed that the surfactant nature, concentration, external phase volume, droplet size reduction method and drug loading concentration can all influence the overall performance of the nanoparticles.
The semi-quantitative solubility study indicates the strong influence of CoQ10 on CsA entrapment which was thought to be due to an increase in the lipophilicity of the overall system. The in vitro dissolution profile indicates the influence of CoQ10 on CsA release (64%) to that of individual particles of CsA, where the release is faster and higher (86%) on 18th day. The attempts to model the encapsulation and release kinetics were successful, offering a possibility to use such models leading to high throughput screening of drugs and their nature, alone or in combination for a particular polymer, if chi-parameters are understood
D D Ankola1, E W Durbin2, G A Buxton3, J Schäfer4, U Bakowsky4 and M N V Ravi Kumar1,5
1 Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, 27 Taylor Street, Glasgow, G4 0NR, UK
2 Department of Physics, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
3 Department of Sciences, Robert Morris University, 6001 University Boulevard, Moon Township, PA 15108, USA
4 Department of Pharmaceutics and Biopharmacy, Philipps Universitt, 35037 Marburg, Germany
Along this line, we attempted to design nano-scale systems for simultaneous encapsulation of cyclosporine A (CsA) and coenzyme Q10 (CoQ10) and model their encapsulation and release kinetics. The in vitro characterization of the co-encapsulated nanoparticles revealed that the surfactant nature, concentration, external phase volume, droplet size reduction method and drug loading concentration can all influence the overall performance of the nanoparticles.
The semi-quantitative solubility study indicates the strong influence of CoQ10 on CsA entrapment which was thought to be due to an increase in the lipophilicity of the overall system. The in vitro dissolution profile indicates the influence of CoQ10 on CsA release (64%) to that of individual particles of CsA, where the release is faster and higher (86%) on 18th day. The attempts to model the encapsulation and release kinetics were successful, offering a possibility to use such models leading to high throughput screening of drugs and their nature, alone or in combination for a particular polymer, if chi-parameters are understood
D D Ankola1, E W Durbin2, G A Buxton3, J Schäfer4, U Bakowsky4 and M N V Ravi Kumar1,5
1 Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, 27 Taylor Street, Glasgow, G4 0NR, UK
2 Department of Physics, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
3 Department of Sciences, Robert Morris University, 6001 University Boulevard, Moon Township, PA 15108, USA
4 Department of Pharmaceutics and Biopharmacy, Philipps Universitt, 35037 Marburg, Germany
Tuesday
Pank1 plays an important role in coenzyme A homeostasis during fasting
Coenzyme A (CoA) is an essential cofactor synthesized in five steps from pantothenate, and pantothenate kinase (PanK) catalyzes the first and most regulated step. The Pank1 gene encodes two of the four PanK isoforms, PanK1 and 1β. Deletion of exon 3 in the mouse Pank1 gene resulted in loss of expression of both isoforms. The liver of the Pank1 knockout animals contained 40% less total CoA, and the knockout mice showed a blunted response to a pyruvate challenge, indicating impairment in gluconeogenesis.
Fasting increases Coenzyme A (CoA)levels to support β-oxidation and gluconeogenesis. Following a 48h fast, the Coenzyme A (CoA) levels increased by 70% (from 122 ± 4 to 207 ± 23 nmoles/mg of tissue) in livers from wild type and by 50% (from 71 ± 7 to 107 ± 11 nmole/mg of tissue) in livers from knockout mice.
Concomitantly, the knockout livers accumulated five times more triglycerides than controls, and the knockout liver homogenates exhibited a decreased rate of palmitic acid oxidation. These results indicate that the reduction in CoA decreases the efficiency of fatty acid β-oxidation, and that in addition to contributing a large portion of the cofactor pool, Pank1 plays an important role in responding to the increased demand for CoA during fasting. We also observed that the Pank1 knockout males are hyperphagic and 15% heavier than controls, which correlated with a 50% lower malonyl-CoA in the hypothalamus. Supported by NIH GM062896, CA21765, and ALSAC
Roberta Leonardi1, Jina Wang1, Karen Miller1, Charles O. Rock1 and Suzanne Jackowski1
1 Infectious Diseases, St. Jude Children's Research Hospital, Memphis, TN
Fasting increases Coenzyme A (CoA)levels to support β-oxidation and gluconeogenesis. Following a 48h fast, the Coenzyme A (CoA) levels increased by 70% (from 122 ± 4 to 207 ± 23 nmoles/mg of tissue) in livers from wild type and by 50% (from 71 ± 7 to 107 ± 11 nmole/mg of tissue) in livers from knockout mice.
Concomitantly, the knockout livers accumulated five times more triglycerides than controls, and the knockout liver homogenates exhibited a decreased rate of palmitic acid oxidation. These results indicate that the reduction in CoA decreases the efficiency of fatty acid β-oxidation, and that in addition to contributing a large portion of the cofactor pool, Pank1 plays an important role in responding to the increased demand for CoA during fasting. We also observed that the Pank1 knockout males are hyperphagic and 15% heavier than controls, which correlated with a 50% lower malonyl-CoA in the hypothalamus. Supported by NIH GM062896, CA21765, and ALSAC
Roberta Leonardi1, Jina Wang1, Karen Miller1, Charles O. Rock1 and Suzanne Jackowski1
1 Infectious Diseases, St. Jude Children's Research Hospital, Memphis, TN
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