Browsing Pathways

The degradation of galactose, also known as Leloir pathway, requires 3 main enzymes once Beta-D-galactose has been converted to galactose through an Aldose-1-epimerase. These are: galactokinase , galactose-1-phosphate uridylyltransferase and UDP-glucose 4-epimerase. Beta-D-galactose can be uptaken from the environment through a galactose proton symporter. It can also be produced by lactose degradation involving a lactose permease to uptake lactose from the environment and a beta-galactosidase to turn lactose into Beta-D-galactose. Galactose is degraded through the following process: Beta-D-galactose is introduced into the cytoplasm through a galactose proton symporter, or it can be synthesized from an alpha lactose that is introduced into the cytoplasm through a lactose permease. Alpha lactose interacts with water through a beta-galactosidase resulting in a beta-D-glucose and beta-D-galactose. Beta-D-galactose is isomerized into D-galactose. D-Galactose undergoes phosphorylation through a galactokinase, hence producing galactose 1 phosphate. On the other side of the pathway, a gluose-1-phosphate (product of the interaction of alpha-D-glucose 6-phosphate with a phosphoglucomutase resulting in a alpha-D-glucose-1-phosphate, an isomer of Glucose 1-phosphate, or an isomer of Beta-D-glucose 1-phosphate) interacts with UTP and a hydrogen ion in order to produce a uridine diphosphate glucose. This is followed by the interaction of galactose-1-phosphate with an established amount of uridine diphosphate glucose through a galactose-1-phosphate uridylyltransferase, which in turn output a glucose-1-phosphate and a uridine diphosphate galactose. The glucose -1-phosphate is transformed into a uridine diphosphate glucose through UTP--glucose-1-phosphate uridylyltransferase. The product, uridine diphosphate glucose, can undergo a reversible reaction in which it can be turned into uridine diphosphategalactose through an UDP-glucose 4-epimerase, and so the cycle can keep going as long as more lactose or galactose is imported into the cell.

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.

The biosynthesis of isoprenoids starts with a D-glyceraldehyde 3-phosphate interacting with a hydrogen ion through a 1-deoxyxylulose-5-phosphate synthase resulting in a carbon dioxide and 1-Deoxy-D-xylulose. The latter compound then interacts with a hydrogen ion through a NADPH driven 1-deoxy-D-xylulose 5-phosphate reductoisomerase resulting in a NADP and a 2-C-methyl-D-erythritol 4-phosphate. The latter compound then interacts with a cytidine triphosphate and a hydrogen ion through a 4-diphosphocytidyl-2C-methyl-D-erythritol synthase resulting in a pyrophosphate and a 4-(cytidine 5'-diphospho)-2-C-methyl-D-erythritol. The latter compound is then phosphorylated through an ATP driven 4-diphosphocytidyl-2-C-methylerythritol kinase resulting in a release of an ADP, a hydrogen ion and a 2-phospho-4-(cytidine 5'-diphospho)-2-C-methyl-D-erythritol. The latter compound then interacts with a 2C-methyl-D-erythritol 2,4-cyclodiphosphate synthase resulting in the release of a 2-C-methyl-D-erythritol-2,4-cyclodiphosphate resulting in the release of a cytidine monophosphate and 2-C-methyl-D-erythritol-2,4-cyclodiphosphate. The latter compound then interacts with a reduced flavodoxin through a 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate synthase resulting in the release of a water molecule, a hydrogen ion, an oxidized flavodoxin and a 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate. The compound 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate can interact with an NADPH,a hydrogen ion through a 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate reductase resulting in a NADP, a water molecule and either a Dimethylallylpyrophosphate or a Isopentenyl pyrophosphate. These two last compounds can be are isomers that can be produced through a isopentenyl diphosphate isomerase. Dimethylallylpyrophosphate interacts with the isopentenyl pyrophosphate through a geranyl diphosphate synthase / farnesyl diphosphate synthase resulting in a pyrophosphate and a geranyl--PP. The latter compound interacts with a Isopentenyl pyrophosphate through a geranyl diphosphate synthase / farnesyl diphosphate synthase resulting in the release of a pyrophosphate and a farnesyl pyrophosphate. The latter compound interacts with isopentenyl pyrophosphate either through a undecaprenyl diphosphate synthase resulting in a release of a pyrophosphate and a di-trans,octa-cis-undecaprenyl diphosphate or through a octaprenyl diphosphate synthase resulting in a pyrophosphate and an octaprenyl diphosphate

Beta-Alanine metabolism starts as a product of aspartate metabolism. Aspartate is decarboxylated by aspartate 1-decarboxylase, releasing carbon dioxide and beta-alanine. Beta-Alanine is then metabolized through a pantothenate synthease resulting in pantothenic acid. Pantothenic acid then undergoes phosphorylation through an ATP-driven pantothenate kinase, resulting in D-4-phosphopantothenate. Pantothenate, vitamin B5, is a precursor for synthesis of 4'-phosphopantetheine moiety of coenzyme A and acyl carrier protein. Plants and microorganisms can synthesize pantothenate de novo, but animals must obtain it from diet. Enzymes of beta-alanine metabolism are targets for anti-microbial drugs.

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.

The biosynthesis of a enterobacterial common antigen can begin with a di-trans,octa-cis-undecaprenyl phosphate interacts with a Uridine diphosphate-N-acetylglucosamine through undecaprenyl-phosphate α-N-acetylglucosaminyl transferase resulting in a N-acetyl-α-D-glucosaminyl-diphospho-ditrans,octacis-undecaprenol and a Uridine 5'-monophosphate. The N-acetyl-α-D-glucosaminyl-diphospho-ditrans,octacis-undecaprenol then reacts with an UDP-ManNAcA from the Amino sugar and nucleotide sugar metabolism pathway. This reaction is metabolized by a UDP-N-acetyl-D-mannosaminuronic acid transferase resulting in a uridine 5' diphosphate, a hydrogen ion and a Undecaprenyl N-acetyl-glucosaminyl-N-acetyl-mannosaminuronate-4-acetamido-4,6-dideoxy-D-galactose pyrophosphate. Glucose 1 phosphate can be metabolize by interacting with a hydrogen ion and a thymidine 5-triphosphate by either reacting with a dTDP-glucose pyrophosphorylase or a dTDP-glucose pyrophosphorylase 2 resulting in the release of a pyrophosphate and a dTDP-D-glucose. The latter compound is then dehydrated through an dTDP-glucose 4,6-dehydratase 2 resulting in water and dTDP-4-dehydro-6-deoxy-D-glucose. The latter compound interacts with L-glutamic acid through a dTDP-4-dehydro-6-deoxy-D-glucose transaminase resulting in the release of oxoglutaric acid and dTDP-thomosamine. The latter compound interacts with acetyl-coa through a dTDP-fucosamine acetyltransferase resulting in a Coenzyme A, a hydrogen Ion and a TDP-Fuc4NAc. Undecaprenyl N-acetyl-glucosaminyl-N-acetyl-mannosaminuronate-4-acetamido-4,6-dideoxy-D-galactose pyrophosphate then interacts with a TDP--Fuc4NAc through a 4-acetamido-4,6-dideoxy-D-galactose transferase resulting in a hydrogen ion, a dTDP and a Undecaprenyl N-acetyl-glucosaminyl-N-acetyl-mannosaminuronate-4-acetamido-4,6-dideoxy-D-galactose pyrophosphate. This compound is then transported through a protein wzxE into the periplasmic space so that it can be incorporated into the outer membrane.

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.

The glyoxylate cycle starts with the interaction of Acetyl-Coa with a water molecule and Oxalacetic acid interact through a Citrate synthase resulting in a release of a coenzyme a and citric acid. The citric acid gets dehydrated through a citrate hydro-lyase resulting in the release of a water molecule and cis-Aconitic acid. The cis-Aconitic acid is then hydrated in an reversible reaction through an aconitate hydratase resulting in an Isocitric acid. The isocitric acid then interacts in a reversible reaction through isocitrate lyase resulting in the release of a succinic acid and a glyoxylic acid. The glyoxylic acid then reacts in a reversible reaction with an acetyl-coa, and a water molecule in a reversible reaction, resulting in a release of a coenzyme A, a hydrogen ion and an L-malic acid. The L-malic acid interacts in a reversible reaction through a NAD driven malate dehydrogenase resulting in the release of NADH, a hydrogen ion and an Oxalacetic acid.

Threhalose biosynthesis begins with an Alpha-D-glucose-1-phosphate interacting with an ATP through a glucose-1-phosphate adenylyltransferase resulting in the release of a pyrophosphate and an ADP-glucose. The latter compound interacts in a reversible reaction with an amylose through a glycogen synthase resulting in the release of an ADP and an amylose. Amylose then interacts in a reversible reaction with 1,4-α-glucan branching enzyme resulting in a glycogen Glycogen can also be produced by a reversible reaction with Amylose through a maltodextrin phosphorylase, releasing a phosphate and a glycogen. Glycogen is then transformed into trehalose through a glycogen debranching enzyme. Alpha Alpha Trehalose can be degraded by reacting with with a water molecule through a cytoplasmic trehalase resulting in the release of a Beta-D-glucose and an Alpha-D-glucose.phosphorylated resulting in a Beta-D-glucose 6-phosphate. This compound is phosphorylated and can then join glycolysis Alpha Alpha Trehalose can be degraded in the periplasmic space by reacting with with a water molecule through a periplasmic trehalase resulting in the release of a Beta-D-glucose and an Alpha-D-glucose. The beta-D-glucose can be transported into the cytosol through a PTS permease where it is phosphorylated resulting in a Beta-D-glucose 6-phosphate. This compound can then join glycolysis

The glyoxylate cycle starts with the interaction of Acetyl-Coa with a water molecule and Oxalacetic acid interact through a Citrate synthase resulting in a release of a coenzyme a and citric acid. The citric acid gets dehydrated through a citrate hydro-lyase resulting in the release of a water molecule and cis-Aconitic acid. The cis-Aconitic acid is then hydrated in an reversible reaction through an aconitate hydratase resulting in an Isocitric acid. The isocitric acid then interacts in a reversible reaction through isocitrate lyase resulting in the release of a succinic acid and a glyoxylic acid. The glyoxylic acid then reacts in a reversible reaction with an acetyl-coa, and a water molecule in a reversible reaction, resulting in a release of a coenzyme A, a hydrogen ion and an L-malic acid. The L-malic acid interacts in a reversible reaction through a NAD driven malate dehydrogenase resulting in the release of NADH, a hydrogen ion and an Oxalacetic acid.