Browsing Pathways

Cyclopropane fatty acids (CFA) are synthesized by the modification of an unsaturated bond of acyl chains of phospholipid bilayers by methylenation via cyclopropane fatty acyl phospholipid synthase. CFA phospholipid synthase is a unique enzyme in that it acts on the nonpolar part of the phospholipids. The bond that is modified is about nine to eleven carbon atoms from the glycerol backbone. S-adenosyl-L-methionine donates a methylene group to the cis double bond of the unsaturated fatty acid. CFA synthase acts on phosphatidylethanolamine, phosphatidylglycerol and phosphatidylcholine. Cyclopropane fatty acids in the cytoplasmic membrane protect cells from ethanol, high osmotic pressure and other environmental stressors.

Cyclopropane fatty acids (CFA) are synthesized by the modification of an unsaturated bond of acyl chains of phospholipid bilayers by methylenation via cyclopropane fatty acyl phospholipid synthase. CFA phospholipid synthase is a unique enzyme in that it acts on the nonpolar part of the phospholipids. The bond that is modified is about nine to eleven carbon atoms from the glycerol backbone. S-adenosyl-L-methionine donates a methylene group to the cis double bond of the unsaturated fatty acid. CFA synthase acts on phosphatidylethanolamine, phosphatidylglycerol and phosphatidylcholine. Cyclopropane fatty acids in the cytoplasmic membrane protect cells from ethanol, high osmotic pressure and other environmental stressors.

In E.coli, trehalose can be only synthesized with high osmolarity, and if the osmolarity is low, then the source of trehalose can be only obtained from external via transportation with trehalose PTS permease. However, sugar can be degraded with both low or high osmolarity in E.coli. Glucokinase can phosphorylate free gluocose into glucose-6-phosphate and both glucose-6-phosphate moieties enter glycolysis.

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.

In E.coli, trehalose can be only synthesized with high osmolarity, and if the osmolarity is low, then the source of trehalose can be only obtained from external via transportation with trehalose PTS permease. However, sugar can be degraded with both low or high osmolarity in E.coli. Glucokinase can phosphorylate free gluocose into glucose-6-phosphate and both glucose-6-phosphate moieties enter glycolysis.

In E.coli, trehalose can be only synthesized with high osmolarity, and if the osmolarity is low, then the source of trehalose can be only obtained from external via transportation with trehalose PTS permease. However, sugar can be degraded with both low or high osmolarity in E.coli. Glucokinase can phosphorylate free gluocose into glucose-6-phosphate and both glucose-6-phosphate moieties enter glycolysis.

2-oxoglutarate dehydrogenase complex is consisted of oxoglutarate decarboxylase, dihydrolipoyl succinyltransferase and dihydrolipoyl dehydrogenase), which is a rate-limiting enzyme of the citric acid cycle (TCA cycle) in prokaryote. The reaction that catalyzed by 2-oxoglutarate dehydrogenase complex can be generalized as 2-oxoglutarate + coenzyme A + NAD+ → succinyl-CoA + CO2 + NADH. During the OGDHC reaction cycle, 2-oxoglutarate is bound and decarboxylated by E1(o), a thiamin-diphosphate cofactor containing enzyme. The succinyl group is transferred to the lipoyl domain of E2(o) where it is carried to the active site and transferred to coenzyme A, forming succinyl-CoA. During this transfer the lipoyl group is reduced to dihydrolipoyl. The succinyl-CoA is released and the lipoyl domain of E2(o) is oxidized by E3 via transfer of protons to NAD, forming NADH and regenerating the lipoyl group back to lipoyllysine for another cycle. Under aerobic growth conditions the OGDHC not only catalyzes a key reaction in the TCA cycle, it also provides succinyl-CoA for methionine and lysine biosynthesis, the latter pathway also leading to peptidoglycan biosynthesis. The synthesis of the OGDHC is repressed by anaerobiosis and is also subject to glucose repression. It is induced by aerobic growth on acetate. (EcoCyc)

2-oxoglutarate dehydrogenase complex is consisted of oxoglutarate decarboxylase, dihydrolipoyl succinyltransferase and dihydrolipoyl dehydrogenase), which is a rate-limiting enzyme of the citric acid cycle (TCA cycle) in prokaryote. The reaction that catalyzed by 2-oxoglutarate dehydrogenase complex can be generalized as 2-oxoglutarate + coenzyme A + NAD+ → succinyl-CoA + CO2 + NADH. During the OGDHC reaction cycle, 2-oxoglutarate is bound and decarboxylated by E1(o), a thiamin-diphosphate cofactor containing enzyme. The succinyl group is transferred to the lipoyl domain of E2(o) where it is carried to the active site and transferred to coenzyme A, forming succinyl-CoA. During this transfer the lipoyl group is reduced to dihydrolipoyl. The succinyl-CoA is released and the lipoyl domain of E2(o) is oxidized by E3 via transfer of protons to NAD, forming NADH and regenerating the lipoyl group back to lipoyllysine for another cycle. Under aerobic growth conditions the OGDHC not only catalyzes a key reaction in the TCA cycle, it also provides succinyl-CoA for methionine and lysine biosynthesis, the latter pathway also leading to peptidoglycan biosynthesis. The synthesis of the OGDHC is repressed by anaerobiosis and is also subject to glucose repression. It is induced by aerobic growth on acetate. (EcoCyc)

2-oxoglutarate dehydrogenase complex is consisted of oxoglutarate decarboxylase, dihydrolipoyl succinyltransferase and dihydrolipoyl dehydrogenase), which is a rate-limiting enzyme of the citric acid cycle (TCA cycle) in prokaryote. The reaction that catalyzed by 2-oxoglutarate dehydrogenase complex can be generalized as 2-oxoglutarate + coenzyme A + NAD+ → succinyl-CoA + CO2 + NADH. During the OGDHC reaction cycle, 2-oxoglutarate is bound and decarboxylated by E1(o), a thiamin-diphosphate cofactor containing enzyme. The succinyl group is transferred to the lipoyl domain of E2(o) where it is carried to the active site and transferred to coenzyme A, forming succinyl-CoA. During this transfer the lipoyl group is reduced to dihydrolipoyl. The succinyl-CoA is released and the lipoyl domain of E2(o) is oxidized by E3 via transfer of protons to NAD, forming NADH and regenerating the lipoyl group back to lipoyllysine for another cycle. Under aerobic growth conditions the OGDHC not only catalyzes a key reaction in the TCA cycle, it also provides succinyl-CoA for methionine and lysine biosynthesis, the latter pathway also leading to peptidoglycan biosynthesis. The synthesis of the OGDHC is repressed by anaerobiosis and is also subject to glucose repression. It is induced by aerobic growth on acetate. (EcoCyc)