Browsing Pathways

Leucine biosynthesis involves a five-step conversion process starting with the valine precursor 2-keto-isovalerate interacting with acetyl-CoA and water through a 2-isopropylmalate synthase resulting in Coenzyme A, hydrogen Ion and 2-isopropylmalic acid. The latter compound reacts with isopropylmalate isomerase which dehydrates the compound resulting in a Isopropylmaleate. This compound reacts with water through a isopropylmalate isomerase resulting in 3-isopropylmalate. This compound interacts with a NAD-driven D-malate / 3-isopropylmalate dehydrogenase results in 2-isopropyl-3-oxosuccinate. This compound interacts spontaneously with hydrogen resulting in the release of carbon dioxide and ketoleucine. Ketoleucine interacts in a reversible reaction with L-glutamic acid through a branched-chain amino-acid aminotransferase resulting in Oxoglutaric acid and L-leucine. L-leucine can then be exported outside the cytoplasm through a transporter: L-amino acid efflux transporter. In the final step, ketoleucine can be catalyzed to form L-leucine by branched-chain amino-acid aminotransferase (IlvE) and tyrosine aminotransferase (TryB). L-Glutamic acid can also be transformed into oxoglutaric acid by these two enzymes. Tyrosine aminotransferase can be suppressed by lecuine, and inhibited by 2-keto-isovarlerate and its end product, tyrosine. 2-ketoisocaproate can not be introduced if 2-keto-isovarlerate inhibit TyrB and IlvE is absent.

Nicotinamide adenine dinucleotide (NAD) can be biosynthesized from L-aspartic acid. This amino acid reacts with oxygen through an L-aspartate oxidase resulting in a hydrogen ion, hydrogen peroxide and an iminoaspartic acid. The latter compound interacts with dihydroxyacetone phosphate through a quinolinate synthase A, resulting in a phosphate, water, and a quinolic acid. Quinolic acid interacts with phosphoribosyl pyrophosphate and hydrogen ion through a quinolinate phosphoribosyltransferase resulting in pyrophosphate, carbon dioxide and nicotinate beta-D-ribonucleotide. The latter is adenylated through an ATP driven nicotinate-mononucleotide adenylyltransferase releasing a pyrophosphate and resulting in a nicotinic acid adenine dinucleotide. Nicotinic acid adenine dinucleotide is processed through an NAD synthetase, NH3-dependent in two different manners. In the first case, Nicotinic acid adenine dinucleotide interacts with ATP, L-glutamine and water through the enzyme and results in hydrogen ion, AMP, pyrophosphate, L-glutamic acid and NAD. In the second case, Nicotinic acid adenine dinucleotide interacts with ATP and ammonium through the enzyme resulting in a pyrophosphate, AMP, hydrogen ion and NAD. NAD then proceeds to regulate its own pathway by repressing L-aspartate oxidase. As a general rule, most prokaryotes utilize the aspartate de novo pathway, in which the nicotinate moiety of NAD is synthesized from aspartate , while in eukaryotes, the de novo pathway starts with tryptophan.

Cardiolipin (CL) is an important component of the inner mitochondrial membrane where it constitutes about 20% of the total lipid composition. It is essential for the optimal function of numerous enzymes that are involved in mitochondrial energy metabolism (Wikipedia). Cardiolipin biosynthesis occurs mainly in the mitochondria, but there also exists an alternative synthesis route for CDP-diacylglycerol that takes place in the endoplasmic reticulum. This second route may supplement this pathway. All membrane-localized enzymes are coloured dark green in the image. First, dihydroxyacetone phosphate (or glycerone phosphate) from glycolysis is used by the cytosolic enzyme glycerol-3-phosphate dehydrogenase [NAD(+)] to synthesize sn-glycerol 3-phosphate. Second, the mitochondrial outer membrane enzyme glycerol-3-phosphate acyltransferase esterifies an acyl-group to the sn-1 position of sn-glycerol 3-phosphate to form 1-acyl-sn-glycerol 3-phosphate (lysophosphatidic acid or LPA). Third, the enzyme 1-acyl-sn-glycerol-3-phosphate acyltransferase converts LPA into phosphatidic acid (PA or 1,2-diacyl-sn-glycerol 3-phosphate) by esterifying an acyl-group to the sn-2 position of the glycerol backbone. PA is then transferred to the inner mitochondrial membrane to continue cardiolipin synthesis. Fourth, magnesium-dependent phosphatidate cytidylyltransferase catalyzes the conversion of PA into CDP-diacylglycerol. Fifth, CDP-diacylglycerol--glycerol-3-phosphate 3-phosphatidyltransferase synthesizes phosphatidylglycerophosphate (PGP). Sixth, phosphatidylglycerophosphatase and protein-tyrosine phosphatase dephosphorylates PGP to form phosphatidylglycerol (PG). Last, cardiolipin synthase catalyzes the synthesis of cardiolipin by transferring a phosphatidyl group from a second CDP-diacylglycerol to PG. It requires a divalent metal cation cofactor.

E. coli lipid A is synthesized on the cytoplasmic surface of the inner membrane. Starting with either the fructose 6-phosphate produced by glycolysis and pyruvate dehydrogenase or obtained from the interaction with D-fructose interacting with a mannose PTS permease. Fructose 6-phosphate interacts with L-glutamine through a D-fructose-6-phosphate aminotransferase resulting into a L-glutamic acid and a glucosamine 6-phosphate. The latter compound is isomerized through a phosphoglucosamine mutase resulting a glucosamine 1-phosphate. This compound is acetylated, interacting with acetyl-CoA through a bifunctional protein glmU resulting in a Coenzyme A, hydrogen ion and N-acetyl-glucosamine 1-phosphate. The latter interacts with UTP and hydrogen ion through the bifunctional protein glmU resulting in a pyrophosphate and a UDP-N-acetylglucosamine. UDP-N-acetylglucosamine iinteracts with (3R)-3-hydroxymyristoyl-[acp] through an UDP-N-acetylglucosamine acyltransferase resulting in a holo-[acp] and a UDP-3-O[(3R)-3-hydroxymyristoyl]-N-acetyl-alpha-D-glucosamine. The latter continues and reacts with water through UDP-3-O-acyl-N-acetylglucosamine deacetylase resulting in an acetic acid and UDP-3-O-(3-hydroxymyristoyl)-α-D-glucosamine. The latter compound interacts with (3R)-3-hydroxymyristoyl-[acp] through UDP-3-O-(R-3-hydroxymyristoyl)-glucosamine N-acyltransferase releasing a hydrogen ion, a holo-acp and UDP-2-N,3-O-bis[(3R)-3-hydroxytetradecanoyl]-α-D-glucosamine. The latter compound is hydrolase by interacting with water and a UDP-2,3-diacylglucosamine hydrolase resulting in UMP, hydrogen ion and 2,3-bis[(3R)-3-hydroxymyristoyl]-α-D-glucosaminyl 1-phosphate. The latter interacts with a UDP-2-N,3-O-bis[(3R)-3-hydroxytetradecanoyl]-α-D-glucosamine through a lipid A disaccharide synthase resulting in a release of UDP, hydrogen ion and a lipid A disaccharide. The lipid A disaccharide is phosphorylated by an ATP mediated tetraacyldisaccharide 4'-kinase resulting in the release of hydrogen ion and lipid IVA. A D-ribulose 5-phosphate is isomerized with D-arabinose 5-phosphate isomerase 2 resulting in a D-arabinose 5-phosphate. D-arabinose 5-phosphate interacts with water and phosphoenolpyruvic acid through a 3-deoxy-D-manno-octulosonate 8-phosphate synthase resulting in the release of phosphate and 3-deoxy-D-manno-octulosonate 8-phosphate. This compound interacts with water through a 3-deoxy-D-manno-octulosonate 8-phosphate phosphatase thus releasing a phosphate and a 3-deoxy-D-manno-octulosonate. The latter compound interacts with CTP through a 3-deoxy-D-manno-octulosonate cytidylyltransferase resulting in a pyrophosphate and CMP-3-deoxy-α-D-manno-octulosonate. CMP-3-deoxy-α-D-manno-octulosonate and lipid IVA interact with each other through a KDO transferase resulting in CMP, hydrogen ion and alpha-Kdo-(2-->6)-lipid IVA. The latter compound reacts with CMP-3-deoxy-α-D-manno-octulosonate through a KDO transferase resulting in a CMP, hydrogen ion, and a a-Kdo-(2->4)-a-Kdo-(2->6)-lipid IVA. The latter compound can either react with a palmitoleoyl-acp through a palmitoleoyl acyltransferase resulting in the release of a holo-acyl carriere protein and a Kdo2-palmitoleoyl-lipid IVa which in turn reacts with a myristoyl-acp through a myristoyl-acp dependent acyltransferase resulting in a release of a holo-acp and a Kdo2-lipid A, cold adapted, or it can interact with a dodecanoyl-[acp] lauroyl acyltransferase resulting in a holo-[acp] and a (KDO)2-(lauroyl)-lipid IVA. The latter compound reacts with a myristoyl-[acp] through a myristoyl-acyl carrier protein (ACP)-dependent acyltransferase resulting in a holo-[acp], (KDO)2-lipid A. The latter compound reacts with ADP-L-glycero-beta-D-manno-heptose through ADP-heptose:LPS heptosyltransferase I resulting hydrogen ion, ADP, heptosyl-KDO2-lipid A. The latter compound interacts with ADP-L-glycero-beta-D-manno-heptose through ADP-heptose:LPS heptosyltransferase II resulting in ADP, hydrogen ion and (heptosyl)2-Kdo2-lipid A. The latter compound UDP-glucose interacts with (heptosyl)2-Kdo2-lipid A resulting in UDP, hydrogen ion and glucosyl-(heptosyl)2-Kdo2-lipid A. Glucosyl-(heptosyl)2-Kdo2-lipid A (Escherichia coli) is phosphorylated through an ATP-mediated lipopolysaccharide core heptose (I) kinase resulting in ADP, hydrogen ion and glucosyl-(heptosyl)2-Kdo2-lipid A-phosphate. The latter compound interacts with ADP-L-glycero-beta-D-manno-heptose through a lipopolysaccharide core heptosyl transferase III resulting in ADP, hydrogen ion, and glucosyl-(heptosyl)3-Kdo2-lipid A-phosphate. The latter compound is phosphorylated through an ATP-driven lipopolysaccharide core heptose (II) kinase resulting in ADP, hydrogen ion and glucosyl-(heptosyl)3-Kdo2-lipid A-bisphosphate. The latter compound interacts with UDP-alpha-D-galactose through a UDP-D-galactose:(glucosyl)lipopolysaccharide-1,6-D-galactosyltransferase resulting in a UDP, a hydrogen ion and a galactosyl-glucosyl-(heptosyl)3-Kdo2-lipid A-bisphosphate. The latter compound interacts with UDP-glucose through a (glucosyl)LPS α-1,3-glucosyltransferase resulting in a hydrogen ion, a UDP and galactosyl-(glucosyl)2-(heptosyl)3-Kdo2-lipid A-bisphosphate. This compound then interacts with UDP-glucose through a UDP-glucose:(glucosyl)LPS α-1,2-glucosyltransferase resulting in UDP, a hydrogen ion and galactosyl-(glucosyl)3-(heptosyl)3-Kdo2-lipid A-bisphosphate. This compound then interacts with ADP-L-glycero-beta-D-manno-heptose through a lipopolysaccharide core biosynthesis; heptosyl transferase IV; probably hexose transferase resulting in a Lipid A-core. A lipid A-core is then exported into the periplasmic space by a lipopolysaccharide ABC transporter. The lipid A-core is then flipped to the outer surface of the inner membrane by the ATP-binding cassette (ABC) transporter, MsbA. An additional integral membrane protein, YhjD, has recently been implicated in LPS export across the IM. The smallest LPS derivative that supports viability in E. coli is lipid IVA. However, it requires mutations in either MsbA or YhjD, to suppress the normally lethal consequence of an incomplete lipid A . Recent studies with deletion mutants implicate the periplasmic protein LptA, the cytosolic protein LptB, and the IM proteins LptC, LptF, and LptG in the subsequent transport of nascent LPS to the outer membrane (OM), where the LptD/LptE complex flips LPS to the outer surface.

NAD molecules have a relatively short half-life. NAD can be degraded by enzymes, and the degraded NAD molecule can be recouped by NAD salvage cycles. NAD salvage cycles can be used for recycling degraded NAD products such as nicotinamide and nicotinamide D-ribonucleotide. NAD salvage cycles can also be used for absorption of exogenous NAD+. NAD reacts spontaneously with water resulting in the release of hydrogen ion, AMP and beta-nicotinamide D-ribonucleotide. This enzyme can either interact spontaneously with water resulting in the release of D-ribofuranose 5-phosphate, hydrogen ion and Nacinamide. On the other hand beta-nicotinamide D-ribonucleotide can also react with water through NMN amidohydrolase resulting in ammonium, and Nicotinate beta-D-ribonucleotide. Also it can interact with water spontaneously resulting in the release of phosphate resulting in a Nicotinamide riboside. Niacinamide interacts with water through a nicotinamidase resulting in a release of ammonium and nicotinic acid. Nicotinic acid interacts with water and phosphoribosyl pyrophosphate through an ATP driven nicotinate phosphoribosyltransferase resulting in the release of ADP, pyrophosphate and phosphate and nicotinate beta-D-ribonucleotide. Nicotinamide riboside interacts with an ATP driven NadR DNA-binding transcriptional repressor and NMN adenylyltransferase (Escherichia coli) resulting in a ADP, hydrogen ion and beta-nicotinamide D-ribonucleotide. The latter interacts with ATP and hydrogen ions through NadR DNA-binding transcriptional repressor and NMN adenylyltransferase resulting in pyrophosphate and NAD. Nicotinate beta-D-ribonucleotide is adenylated through the interaction with ATP and a hydrogen ion through a nicotinate-mononucleotide adenylyltransferase resulting in pyrophosphate and Nicotinic acid adenine dinucleotide. Nicotinic acid adenine dinucleotide interacts with L-glutamine and water through an ATP driven NAD synthease, NH3-dependent resulting in AMP, pyrophosphate, hydrogen ion, L-glutamic acid and NAD.

Cardiolipin (CL) is an important component of the inner mitochondrial membrane where it constitutes about 20% of the total lipid composition. It is essential for the optimal function of numerous enzymes that are involved in mitochondrial energy metabolism (Wikipedia). Cardiolipin biosynthesis occurs mainly in the mitochondria, but there also exists an alternative synthesis route for CDP-diacylglycerol that takes place in the endoplasmic reticulum. This second route may supplement this pathway. All membrane-localized enzymes are coloured dark green in the image. First, dihydroxyacetone phosphate (or glycerone phosphate) from glycolysis is used by the cytosolic enzyme glycerol-3-phosphate dehydrogenase [NAD(+)] to synthesize sn-glycerol 3-phosphate. Second, the mitochondrial outer membrane enzyme glycerol-3-phosphate acyltransferase esterifies an acyl-group to the sn-1 position of sn-glycerol 3-phosphate to form 1-acyl-sn-glycerol 3-phosphate (lysophosphatidic acid or LPA). Third, the enzyme 1-acyl-sn-glycerol-3-phosphate acyltransferase converts LPA into phosphatidic acid (PA or 1,2-diacyl-sn-glycerol 3-phosphate) by esterifying an acyl-group to the sn-2 position of the glycerol backbone. PA is then transferred to the inner mitochondrial membrane to continue cardiolipin synthesis. Fourth, magnesium-dependent phosphatidate cytidylyltransferase catalyzes the conversion of PA into CDP-diacylglycerol. Fifth, CDP-diacylglycerol--glycerol-3-phosphate 3-phosphatidyltransferase synthesizes phosphatidylglycerophosphate (PGP). Sixth, phosphatidylglycerophosphatase and protein-tyrosine phosphatase dephosphorylates PGP to form phosphatidylglycerol (PG). Last, cardiolipin synthase catalyzes the synthesis of cardiolipin by transferring a phosphatidyl group from a second CDP-diacylglycerol to PG. It requires a divalent metal cation cofactor.

Glycolic acid is introduced into the cytoplasm through either a glycolate / lactate:H+ symporter or a acetate / glycolate transporter. Once inside, glycolic acid reacts with an oxidized electron-transfer flavoprotein through a glycolate oxidase resulting in a reduced acceptor and glyoxylic acid. Glyoxylic acid can also be obtained from the introduction of glyoxylic acid. It can also be obtained from the metabolism of (S)-allantoin. S-allantoin is introduced into the cytoplasm through a purine and pyrimidine transporter(allantoin specific). Once inside, the compound reacts with water through a allantoinase resulting in hydrogen ion and allantoic acid. Allantoic acid then reacts with water and hydrogen ion through a allantoate amidohydrolase resulting in a carbon dioxide, ammonium and S-ureidoglycine. The latter compound reacts with water through a S-ureidoglycine aminohydrolase resulting in ammonium and S-ureidoglycolic acid which in turn reacts with a Ureidoglycolate lyase resulting in urea and glyoxylic acid. Glyoxylic acid can either be metabolized into L-malic acid by a reaction with acetyl-CoA and Water through a malate synthase G which also releases hydrogen ion and Coenzyme A. L-malic acid is then incorporated into the TCA cycle. Glyoxylic acid can also be metabolized by glyoxylate carboligase, releasing a carbon dioxide and tartronate semialdehyde. The latter compound is then reduced by an NADH driven tartronate semialdehyde reductase 2 resulting in glyceric acid. Glyceric acid is phosphorylated by a glycerate kinase 2 resulting in a 3-phosphoglyceric acid. This compound is then integrated into various other pathways: cysteine biosynthesis, serine biosynthesis and glycolysis and pyruvate dehydrogenase.

Cardiolipin (CL) is an important component of the inner mitochondrial membrane where it constitutes about 20% of the total lipid composition. It is essential for the optimal function of numerous enzymes that are involved in mitochondrial energy metabolism (Wikipedia). Cardiolipin biosynthesis occurs mainly in the mitochondria, but there also exists an alternative synthesis route for CDP-diacylglycerol that takes place in the endoplasmic reticulum. This second route may supplement this pathway. All membrane-localized enzymes are coloured dark green in the image. First, dihydroxyacetone phosphate (or glycerone phosphate) from glycolysis is used by the cytosolic enzyme glycerol-3-phosphate dehydrogenase [NAD(+)] to synthesize sn-glycerol 3-phosphate. Second, the mitochondrial outer membrane enzyme glycerol-3-phosphate acyltransferase esterifies an acyl-group to the sn-1 position of sn-glycerol 3-phosphate to form 1-acyl-sn-glycerol 3-phosphate (lysophosphatidic acid or LPA). Third, the enzyme 1-acyl-sn-glycerol-3-phosphate acyltransferase converts LPA into phosphatidic acid (PA or 1,2-diacyl-sn-glycerol 3-phosphate) by esterifying an acyl-group to the sn-2 position of the glycerol backbone. PA is then transferred to the inner mitochondrial membrane to continue cardiolipin synthesis. Fourth, magnesium-dependent phosphatidate cytidylyltransferase catalyzes the conversion of PA into CDP-diacylglycerol. Fifth, CDP-diacylglycerol--glycerol-3-phosphate 3-phosphatidyltransferase synthesizes phosphatidylglycerophosphate (PGP). Sixth, phosphatidylglycerophosphatase and protein-tyrosine phosphatase dephosphorylates PGP to form phosphatidylglycerol (PG). Last, cardiolipin synthase catalyzes the synthesis of cardiolipin by transferring a phosphatidyl group from a second CDP-diacylglycerol to PG. It requires a divalent metal cation cofactor.

Nicotinamide adenine dinucleotide (NAD) can be biosynthesized from L-aspartic acid. This amino acid reacts with oxygen through an L-aspartate oxidase resulting in a hydrogen ion, hydrogen peroxide and an iminoaspartic acid. The latter compound interacts with dihydroxyacetone phosphate through a quinolinate synthase A, resulting in a phosphate, water, and a quinolic acid. Quinolic acid interacts with phosphoribosyl pyrophosphate and hydrogen ion through a quinolinate phosphoribosyltransferase resulting in pyrophosphate, carbon dioxide and nicotinate beta-D-ribonucleotide. The latter is adenylated through an ATP driven nicotinate-mononucleotide adenylyltransferase releasing a pyrophosphate and resulting in a nicotinic acid adenine dinucleotide. Nicotinic acid adenine dinucleotide is processed through an NAD synthetase, NH3-dependent in two different manners. In the first case, Nicotinic acid adenine dinucleotide interacts with ATP, L-glutamine and water through the enzyme and results in hydrogen ion, AMP, pyrophosphate, L-glutamic acid and NAD. In the second case, Nicotinic acid adenine dinucleotide interacts with ATP and ammonium through the enzyme resulting in a pyrophosphate, AMP, hydrogen ion and NAD. NAD then proceeds to regulate its own pathway by repressing L-aspartate oxidase. As a general rule, most prokaryotes utilize the aspartate de novo pathway, in which the nicotinate moiety of NAD is synthesized from aspartate , while in eukaryotes, the de novo pathway starts with tryptophan.

NAD molecules have a relatively short half-life. NAD can be degraded by enzymes, and the degraded NAD molecule can be recouped by NAD salvage cycles. NAD salvage cycles can be used for recycling degraded NAD products such as nicotinamide and nicotinamide D-ribonucleotide. NAD salvage cycles can also be used for absorption of exogenous NAD+. NAD reacts spontaneously with water resulting in the release of hydrogen ion, AMP and beta-nicotinamide D-ribonucleotide. This enzyme can either interact spontaneously with water resulting in the release of D-ribofuranose 5-phosphate, hydrogen ion and Nacinamide. On the other hand beta-nicotinamide D-ribonucleotide can also react with water through NMN amidohydrolase resulting in ammonium, and Nicotinate beta-D-ribonucleotide. Also it can interact with water spontaneously resulting in the release of phosphate resulting in a Nicotinamide riboside. Niacinamide interacts with water through a nicotinamidase resulting in a release of ammonium and nicotinic acid. Nicotinic acid interacts with water and phosphoribosyl pyrophosphate through an ATP driven nicotinate phosphoribosyltransferase resulting in the release of ADP, pyrophosphate and phosphate and nicotinate beta-D-ribonucleotide. Nicotinamide riboside interacts with an ATP driven NadR DNA-binding transcriptional repressor and NMN adenylyltransferase (Escherichia coli) resulting in a ADP, hydrogen ion and beta-nicotinamide D-ribonucleotide. The latter interacts with ATP and hydrogen ions through NadR DNA-binding transcriptional repressor and NMN adenylyltransferase resulting in pyrophosphate and NAD. Nicotinate beta-D-ribonucleotide is adenylated through the interaction with ATP and a hydrogen ion through a nicotinate-mononucleotide adenylyltransferase resulting in pyrophosphate and Nicotinic acid adenine dinucleotide. Nicotinic acid adenine dinucleotide interacts with L-glutamine and water through an ATP driven NAD synthease, NH3-dependent resulting in AMP, pyrophosphate, hydrogen ion, L-glutamic acid and NAD.