Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.3.3.1 (citrate synthase)
 4,488 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The malate synthase activity detectable in crude extracts of Pseudomonas AM1 has been shown to be due to a coupling of a malyl-CoA hydrolase with malyl-CoA lyase and not due to a discrete malate synthase enzyme. The partial purification of this malyl-CoA hydrolase from Pseudomonas AM1 has shown that it is distinct from citrate synthase which also hydrolyses malyl-CoA. The malyl-CoA hydrolase has a low Km for malyl-CoA (7-0 muM). A mutant of Pseudomonas AM1, ICT51 (Taylor & Anthony, 1975), which is unable to grow on ethanol, malonate or 3-hydroxybutyrate, has been shown to have an altered malyl-CoA hydrolase with a Km for malyl-CoA 30 times higher than that of the enzyme present in the wild-type organism. Two classes of revertants to growth on these substrates have been isolated: (i) those with a malyl-CoA hydrolase of similar Km to the wild-type and (ii) those in which the malyl-CoA hydrolase activity remains the same as in the mutant ICT51. The nature of the mutation leading to the latter class of revertants is unknown.
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PMID:Synthesis and hydrolysis of malyl-coenzyme A by Pseudomonas AM1: an apparent malate synthase activity. 95 73

The alpha-ketoglutarate dehydrogenase complex of either pig heart or Escherichia coli catalyzes a NAD- and CoASH-dependent oxidation of 2-keto-4-hydroxyglutarate which is stereoselective toward the L-isomer of this hydroxyketo acid. L-Malyl-CoA is the product of the reaction; the evidence includes observing (a) a steady increase in absorbance at 230 nm during the oxidation of 2-keto-4-hydroxyglutarate, (b) a positive response of oxidation reaction mixtures to neutral hydroxylamine, (c) loss of the two foregoing results concomitant with release of thiol-reacting material and the formation of free malate when reaction mixtures are heated, (d) formation of a hydroxamate which has chromatographic mobilities identical to that of chemically synthesized malate hydroxamate, (e) enzymatic formation of a radioactive product from 14C-labeled 2-keto-4-hydroxyglutarate which co-migrates with chemically synthesized malyl-CoA, and (f) hydrolysis of the product by citrate synthase, an enzyme absolutely specific for citryl-CoA and L-malyl-CoA. A 1:1:1 stoichiometric relationship exists between the amount of 2-keto-4-hydroxyglutarate oxidized, NAD reduced, and malate (or malyl-CoA) formed. Results from studies in which either 14C-labeled 2-keto-4-hydroxyglutarate, pyruvate, or glyoxylate is incubated with mixtures of purified enzymes or extracts of E. coli support the suggestion that the aldolase which preferentially catalyzes formation of L-2-keto-4-hydroxyglutarate from pyruvate plus glyoxylate in E. coli is coupled with the oxidative decarboxylation of this substrate, as reported here, and other enzymes in a multistep pyruvate-catalyzed cyclic oxidation of glyoxylate.
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PMID:Malyl-CoA formation in the NAD-, CoASH-, and alpha-ketoglutarate dehydrogenase-dependent oxidation of 2-keto-4-hydroxyglutarate. Possible coupled role of this reaction with 2-keto-4-hydroxyglutarate aldolase activity in a pyruvate-catalyzed cyclic oxidation of glyoxylate. 638 79

Chemically and stereochemically pure (3S)-citryl-CoA was prepared enzymically and used as a substrate for citrate synthase to investigate the previously determined unexpectedly low rate of hydrolysis of the (3RS)-substrate. The unnatural R-diastereomer of this mixture is not inhibitory. At low enzyme concentrations the rate of citryl-CoA hydrolysis was linear until the reaction went near to completion; the hydrolysis approached Michaelis-Menten kinetics at high enzyme concentrations. In between these concentration extremes a biphasic rate dependence was detectable, where a fast initial phase lasting a few seconds was followed by a slow steady-state phase. Citrate synthase was characterized as a hysteretic enzyme existing in two interconvertible forms, which were designated according to their functions as hydrolase E and ligase E'. The hysteretic behaviour originates in the cleavage of citryl-CoA to acetyl-CoA and oxaloacetate. This reaction occurs on the ligase form E', which represents a trap for enzyme form E, the hydrolase. The conclusions given above are strengthened by the ordinary hydrolysis kinetics of (2S)-malyl-CoA, a substrate that is not subject to cleavage of the C-C bond on the synthase. The results satisfy the kinetic criterion for citryl-CoA being an intermediate of the physiological synthase reaction and, therefore, establish the oscillation of the synthase between hydrolase and ligase states during the catalytic cycle. A disorganization of these oscillations can be achieved by limited tryptic proteolysis of the synthase.
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PMID:Hysteretic behaviour of citrate synthase. Alternating sites during the catalytic cycle. 686 48