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 synthesis of ketone bodies by intact isolated rat-liver mitochondria has been studied at varying rates of acetyl-CoA production and of acetyl-CoA utilization in the Krebs cycle. Factors which enhanced the rate of acetyl-CoA production caused an increase in the fraction of acetyl-CoA which was incorporated into ketone bodies. On the other hand, it was found that factors which stimulated the formation of citrate lowered the relative rate of ketogenesis. It is concluded that acetyl-CoA is preferentially used for citrate synthesis, if the level of oxaloacetate in the mitochondrial matrix space is adequate. The intramitochondrial level of oxaloacetate, which is determined by the malate concentration and the ratio of NADH over NAD+, is the main factor controlling the rate of citrate synthesis. The ATP/ADP ratio per se does not affect the activity of citrate synthase in this in vitro system. Ketogenesis can be described as an overflow of acetyl-groups: Ketone-body formation is stimulated only when the rate of acetyl-CoA production increases beyond the capacity for citrate synthesis. The interaction between fatty acid oxidation and pyruvate metabolism and the effects of long-chain acyl-CoA on mitochondrial metabolism are discussed. Ketone bodies which were generated during the oxidation of [1-14C] fatty acids were preferentially labelled in their carboxyl group. This carboxyl group had the same specific activity as the acetyl-CoA pool, whereas the specific activity of the acetone moiety of acetoacetate was much lower, especially at low rates of ketone-body formation. The activities of acetoacetyl-CoA deacylase and the hydroxymethylglutaryl-CoA (HMG-CoA) pathway were compared in soluble and mitochondrial fractions of rat- and cow-liver in different ketotic states. In rat-liver mitochondria, both pathways of acetoacetate synthesis were stimulated upon starvation or in alloxan diabetes. In cow liver, only the HMG-CoA pathway was increased during ketosis in the mitochondrial as well as in the soluble fraction.
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PMID:Aspects of ketogenesis: control and mechanism of ketone-body formation in isolated rat-liver mitochondria. 119 5

3-Hydroxy-3-methylglutaryl-CoA lyase, which performs the cleavage of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) to acetoacetate and acetyl-CoA by a Claisen-type reaction, also catalyzes enolization of acetyl-CoA. The rate of detritiation of methyl-labeled acetyl-CoA is proportional to enzyme concentration and is diminished by an antiserum that also inhibits the cleavage reaction. The tritium-exchange reaction requires both divalent cation and acetoacetate. An analogue of HMG-CoA, 3-hydroxyglutaryl-CoA, was prepared by reaction of acetonedicarboxylic anhydride with CoASH and reduction of the ketoacyl-CoA product with cyanohydridoborate. While 3-hydroxyglutaryl-CoA does not appear to be a substrate for HMG-CoA lyase, it competitively inhibits both the cleavage reaction (Ki = 50 microM) and the tritium exchange from acetyl-CoA (Ki = 95 microM). Agreement between the Ki values measured for cleavage and for tritium exchange supports the hypothesis that the slow tritium exchange is a lyase-dependent reaction. Initial attempts to demonstrate complete reversibility of the cleavage reaction have not been successful. However, the data suggest that the cleavage of HMG-CoA is at least partially reversible and indicate that enolization of acetyl-CoA may be dependent upon a conformational change of HMG-CoA lyase, induced by binding of acetoacetate, in a manner analogous to the keto acid dependent tritium exchange catalyzed by malate synthase and citrate synthase.
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PMID:3-hydroxy-3-methylglutaryl-CoA lyase: catalysis of acetyl coenzyme A enolization. 686 Jun 31

Sulfoxides and sulfones were prepared by specific oxidation of 3-hydroxy-3-methylglutaryl-CoA-analogue CoA-thioether derivatives and their kinetic properties were determined with 3-hydroxy-3-methylglutaryl-CoA reductase. The oxidized CoA-thioether derivatives with a hydroxyl group at C3 were powerful competitive inhibitors, their Ki values being much smaller than the Km for 3-hydroxy-3-methylglutaryl-CoA. Sulfoxides and sulfones of substrate analogues of citrate synthase were also prepared. When tested in the appropriate reaction with citrate synthase, the sulfoxide and sulfone derivatives were competitive inhibitors, but their Ki values were greater than the Km values of the corresponding unmodified substrates.
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PMID:Inhibition of 3-hydroxy-3-methylglutaryl-CoA reductase and citrate synthase by sulfoxides and sulfones of substrate-analogue CoA-thioether derivatives. 785 98

3-Hydroxy-3-methylglutaryl-CoA synthase (HMGS), EC 4.1.3.5, is an essential enzyme in rubber biosynthesis in Hevea brasiliensis. We have isolated a new cDNA encoding HMGS in H. brasiliensis. The full-length hmgs2 consists of 1,916-bp and encodes a protein of 464 amino acids with a predicted molecular mass of 51.27 kDa and an isoelectric point of 6.02. In comparison, HMGS1 and HMGS2 show 92% and 94% nucleotide and amino acid sequence identities, respectively. Semiquantitative RT-PCR analysis indicates that the hmgs2 is more highly expressed in laticifer and petiole than in leaves. Sequence searching and alignment revealed that HMGS is a distant relative of the condensing enzyme; beta-ketoacyl acyl carrier protein synthase III (ACP synthase III), EC 2.3.1.41, identified three completely conserved residues; Cys(117), His(247), and Asn(326). The relationship was greatly strengthened by making a proper alignment of numerous sequences of both HMGS and ACP synthase III. The same Cys(117), His(247), and Asn(326) absolutely conserved in both groups play a catalytic role in ACP synthase III, while such a role of Cys and His has only been reported for HMGS. According to site-directed mutagenesis, the expressed wild-type enzyme shows comparable level with mutant proteins. The mutation of Cys(117) and Asn(326) affects the HMGS activity, indicating that Cys(117) and Asn(326) are important amino acids for the catalytic activity of HMGS. A phylogenetic tree constructed on the basis of proper multiple alignment indicates that HMGS1 and HMGS2 result from recent gene duplication. This is also the case for HMGS and ACP synthase III, which appear to have arisen from an ancient gene duplication event of an ancestral condensing enzyme. Therefore, a possible secondary structure of HMGS could be predicted based on the Protein Data Bank information of ACP synthase III.
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PMID:Molecular cloning of a new cDNA and expression of 3-hydroxy-3-methylglutaryl-CoA synthase gene from Hevea brasiliensis. 1574 97