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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)

When baker's yeast spheroplasts were lysed by mild osmotic shock, practically all of the isopropylmalate isomerase and the beta-isopropylmalate dehydrogenase was released into the 30,000 x g supernatant fraction, as was the cytosol marker enzyme, glucose-6-phosphate dehydrogenase. alpha-Isopropylmalate synthase, however, was not detected in the initial supernatant, but could be progressively solubilized by homogenization, appearing more slowly than citrate synthase but faster than cytochrome oxidase. Of the total glutamate-alpha-ketoisocaproate transaminase activity, approximately 20% was in the initial soluble fraction, whereas solubilization of the remainder again required homogenization of the spheroplast lysate. Results from sucrose density gradient centrifugation of a cell-free particulate fraction and comparison with marker enzymes suggested that alpha-isopropylmalate synthase was located in the mitochondria. It thus appears that, in yeast, the first specific enzyme in the leucine biosynthetic pathway (alpha-isopropylmalate synthase) is particulate, whereas the next two enzymes in the pathway (isopropylmalate isomerase and beta-isopropylmalate dehydrogenase) are "soluble," with glutamate-alpha-ketoisocaproate transaminase activity being located in both the cytosol and particulate cell fractions.
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PMID:Subcellular localization of the leucine biosynthetic enzymes in yeast. 435 81

Cell-free extracts of Acetobacter suboxydans were prepared which were capable of condensing alpha-ketoisovalerate with (14)C-labeled acetyl-coenzyme A to yield (14)C-labeled alpha-isopropylmalate. The product of the reaction was isolated by paper and column chromatography and was characterized by recrystallization with synthetic alpha-isopropylmalic acid to constant specific radioactivity. The formation of alpha-isopropylmalate by extracts of A. suboxydans plus the ability of the organism to grow in a simple glucose-glycerol medium containing glutamic acid as the only amino acid indicate that the pathway for leucine biosynthesis shown to exist in yeast and Salmonella typhimurium also occurs in A. suboxydans. As a comparison, the condensation of oxalacetate and ((14)C) acetyl-coenzyme A to yield ((14)C) citric acid was shown, by similar means, to occur in A. suboxydans. This is of interest since the existence of this classical condensing enzyme has hitherto not been demonstrated in this organism. This reaction was further demonstrated in cell-free extracts of A. suboxydans by means of a spectrophotometric assay at 232 mmu which measured the cleavage of the carbon-sulfur bond of acetyl-coenzyme A in the presence of oxalacetate. Comparison of the specific activities of crude cell-free extracts indicated a much more extensive occurrence of this reaction in yeast than in A. suboxydans.
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PMID:Biosynthesis of alpha-isopropylmalic and citric acids in Acetobacter suboxydans. 603 58