Browsing Pathways

Glycolysis is a metabolic pathway consisting of ten reactions that convert glucose to pyruvate, releasing energy to form ATP and NADH. It occurs in two phases: the chemical priming phase and the energy-yielding phase. In the priming phase, D-glucose, which can be imported or derived from galactose metabolism, is phosphorylated to glucose-6-phosphate by a hexokinase-like enzyme, using ATP. This is then converted to fructose-6-phosphate, which is further phosphorylated to fructose-1,6-bisphosphate by 6-phosphofructokinase, also using ATP. Aldolase then splits fructose-1,6-bisphosphate into dihydroxyacetone phosphate and glyceraldehyde-3-phosphate, which can interconvert via triosephosphate isomerase. In the energy-yielding phase, glyceraldehyde-3-phosphate is converted to 1,3-bisphosphoglycerate by glyceraldehyde-3-phosphate dehydrogenase, producing NADH in the process. ATP is generated when 1,3-bisphosphoglycerate is converted to 3-phosphoglycerate. Further steps involve the conversion of 3-phosphoglycerate to 2-phosphoglycerate by phosphoglycerate mutase, followed by conversion to phosphoenolpyruvate by enolase. Finally, pyruvate kinase converts phosphoenolpyruvate to pyruvate, producing ATP in the process. Pyruvate then participates in further metabolic pathways, including pyruvate metabolism, tyrosine metabolism, and the synthesis of pantothenate and CoA.

The degradation of of adenosine nucleotides starts with AMP reacting with water through a nucleoside monophosphate phosphatase results in the release of phosphate and a adenosine. Adenosine reacts with water and hydrogen ion through an adenosine deaminase resulting in the release of ammonium and a inosine. Inosine reacts with phosphate through a inosine phosphorylase resulting in the release of an alpha-D-ribose-1-phosphate and an hypoxanthine. Hypoxanthine reacts with a water molecule and a NAD molecule through an hypoxanthine hydroxylase resulting in the release of an hydrogen ion, an NADH and a xanthine. Xanthine in turn is degraded by reacting with a water molecule and a NAD through xanthine NAD oxidoreductase resulting in the release of NADH, a hydrogen ion and urate.

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.

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.

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. The pathway can start from the fructose 6-phosphate that is either produced in the glycolysis and pyruvate dehydrogenase or be 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. This compound interact with UTP and hydrogen ion through the bifunctional protein glmU resulting in a pyrophosphate and a UDP-N-acetylglucosamine. This compound interacts 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. This compound interacts 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. This last compound then 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 to result in a D-arabinose 5-phosphate. This compounds 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.

This pathway demonstrates the degradation of extracellular putrescine in E.coli. Putrescine is imported by putrescine transporter (encoded by puuP gene). Putrescine is γ-glutamylated by activation of ATP which generates γ-glutamyl-putrescine, phosphate, and ADP. γ-glutamyl-putrescine is oxidized by gamma-glutamylputrescine oxidoreductase to form γ-glutamyl-γ-butyraldehyde, also produce ammonium and water. Gamma-glutamyl-gamma-aminobutyraldehyde dehydrogenase dehydrogenates γ-glutamyl-γ-butyraldehyde to γ-glutamyl-γ-aminobutyrate, which is then dehydrogenated into γ-Aminobutyric acid and L-Glutamic acid by γ-glutamyl-γ-aminobutyrate hydrolase.

Most bacteria, including Escherichia coli, are composed of murein which protects and stabilizes the cell wall. Over half of the murein is broken down by Escherichia coli and recycled for the next generation. The main muropeptide is GlcNAc-anhydro-N-acetylmuramic acid (anhMurNAc)-l-Ala-γ-d-Glu-meso-Dap-d-Ala which enters the cytoplasm by AmpG protein. The peptide is then released from the muropeptide. 1,6-Anhydro-N-acetylmuramic acid (anhMurNAc) is recycled by its conversion to N-acetylglucosamine-phosphate (GlcNAc-P). The sugar is phosphorylated by anhydro-N-acetylmuramic acid kinase (AnmK) to produce MurNAc-P. Etherase cleaves MurNAc-P to produce N-acetyl-D-glucosamine 6-phosphate. The product can undergo further degradation or be recycled into peptidoglycan monomers. The pathway's final product is a peptidoglycan biosynthesis precursor, UDP-N-acetyl-α-D-muramate. The enzyme muropeptide ligase (mpl), attaches the recovered Ala-Glu-DAP tripeptide to the precursor UDP-N-acetyl-α-D-muramate to return to the peptide to the peptidoglycan biosynthetic pathway to synthesize the cell wall.

The reaction of pyruvate to cytochrome bd terminal oxidase electron transfer starts with 2 pyruvate and 2 water molecules reacting in a pyruvate oxidase resulting in the release of 4 electrons into the inner membrane, and releasing 2 carbon dioxide molecules , 2 acetate and 4 hydrogen ion into the cytosol. 2 ubiquinone,4 hydrogen ion and 4 electron ion react resulting in the release of 2 ubiquinol . The 2 ubiquinol in turn release 4 hydrogen ions into the periplasmic space through a cytochrome bd-I terminal oxidase and releasing 4 electrons through the enzyme. Oxygen and 4 hydrogen ion reacts with the 4 electrons resulting in 2 water molecules.

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.