Browsing Pathways

Escherichia coli can solely use D-galactonate as a carbon and energy source. The initial step, after the transport of galactonic acid into the cell is the dehydration of D-galactonate to 2-dehydro-3-deoxy-D-galactonate by D-galactonate dehydratase. Subsequent phosphorylation by 2-dehydro-3-deoxygalactonate kinase and aldol cleavage by 2-oxo-3-deoxygalactonate 6-phosphate aldolase produces pyruvate and D-glyceraldehyde-3-phosphate, which enter central metabolism. Galactitol can also be utilized by E. coli K-12 as the sole source of carbon and energy. Each enters the cell via a specific phosphotransferase system, so the first intracellular species is D-galactitol-1-phosphate or D-galactitol-6-phosphate, which are identical. This sugar alcohol phosphate becomes the substrate for a dehydrogenase that oxidizes its 2-alcohol group to a keto group. Galactitol-1-phosphate is dehydrogenated to tagatose-6-phosphate which is then acted on by a kinase and an aldose and eventually is converted to glycolysis intermediates.

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.

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.

D-allose can be used as source of carbon for E.coli. D-allose is imported into E.coli by D-allose ABC transporter without phosphorylation. Allose-6-phosphate isomerase and allulose-6-phosphate 3-epimerase catalyze the remaining reactions resulting in D-allulose 6 phosphate and Beta-D-fructofuranose 6-phosphate respectively. Once Beta D fructofuranose 6-phosphate is synthesized, it can be used in the glycolysis and pyruvatedehydrogenase pathway.

D-allose can be used as source of carbon for E.coli. D-allose is imported into E.coli by D-allose ABC transporter without phosphorylation. Allose-6-phosphate isomerase and allulose-6-phosphate 3-epimerase catalyze the remaining reactions resulting in D-allulose 6 phosphate and Beta-D-fructofuranose 6-phosphate respectively. Once Beta D fructofuranose 6-phosphate is synthesized, it can be used in the glycolysis and pyruvatedehydrogenase pathway.

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.

Escherichia coli can solely use D-galactonate as a carbon and energy source. The initial step, after the transport of galactonic acid into the cell is the dehydration of D-galactonate to 2-dehydro-3-deoxy-D-galactonate by D-galactonate dehydratase. Subsequent phosphorylation by 2-dehydro-3-deoxygalactonate kinase and aldol cleavage by 2-oxo-3-deoxygalactonate 6-phosphate aldolase produces pyruvate and D-glyceraldehyde-3-phosphate, which enter central metabolism. Galactitol can also be utilized by E. coli K-12 as the sole source of carbon and energy. Each enters the cell via a specific phosphotransferase system, so the first intracellular species is D-galactitol-1-phosphate or D-galactitol-6-phosphate, which are identical. This sugar alcohol phosphate becomes the substrate for a dehydrogenase that oxidizes its 2-alcohol group to a keto group. Galactitol-1-phosphate is dehydrogenated to tagatose-6-phosphate which is then acted on by a kinase and an aldose and eventually is converted to glycolysis intermediates.