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)

An isolated single rat hindlimb muscle preparation was used to examine the influence of exercise training on leucine metabolism during steady-state conditions at rest and during isometric contractions. Treadmill training increased the activity of citrate synthase in the hindlimb muscle by 40-45%. Leucine oxidation, measured as the rate of alpha-decarboxylation, was not different between trained (2.28 +/- 0.15 nmol.min-1.g-1, n = 9) and control (2.57 +/- 0.20, n = 9) muscle at rest. In addition, successive 40-min contraction periods at 15 and 45 tetani/min induced similar increases (50 and 100%, respectively) in leucine oxidation in both groups. However, trained muscle maintained a greater tension output (P less than 0.05) during contractions and exhibited a greater oxygen consumption (VO2) (P less than 0.05) during 45 tetani/min. Thus the rate of leucine oxidation, relative to VO2, was less (P less than 0.05) in the trained group. This response was probably related to differences in intracellular factors modulating branched-chain alpha-keto acid dehydrogenase, the rate-limiting step in leucine oxidation. Although our observed rates of muscle leucine alpha-decarboxylation can reasonably account for the rates of whole-body leucine alpha-decarboxylation of nontrained individuals found during steady-state tracer studies in vivo, this is less reasonably the case for the trained group. This suggests that a greater rate of leucine oxidation by nonmuscle tissues (e.g., liver) may occur in trained compared with nontrained individuals.
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PMID:Effect of endurance training on leucine metabolism in perfused rat skeletal muscle. 342 11

The activities of key enzymes in the valine catabolic pathway--branched-chain aminotransferase, branched-chain alpha-keto acid dehydrogenase complex, methacrylyl (MC)-coenzyme A (CoA) hydratase (crotonase), and 3-hydroxyisobutyryl-CoA (HIB-CoA) hydrolase--were measured in normal and cirrhotic human livers. Unlike rat liver, which does not contain branched-chain aminotransferase, the aminotransferase activity in the normal liver was measurable and is increased somewhat in cirrhosis of the human liver. The total activity of branched-chain alpha-keto acid dehydrogenase complex in the normal human liver was approximately 1% of that in rat liver, and 20% to 30% of the complex was in the active form in both normal and cirrhotic livers. Only the actual activity of the enzyme was significantly decreased by cirrhosis. These results suggest that human liver is less active than rat liver in the catabolism of branched-chain amino and alpha-keto acids. Activities of MC-CoA hydratase and HIB-CoA hydrolase in human liver were very high compared with that of branched-chain alpha-keto acid dehydrogenase complex, suggesting an important role for these enzymes in catabolism of a potentially toxic compound, MC-CoA, formed as an intermediate in the catabolism of valine and isobutyrate. Cirrhosis resulted in a significant decrease in HIB-CoA hydrolase activity but had no effect on the citrate synthase activity, suggesting that the decrease in HIB-CoA hydrolase activity does not reflect a general decrease in mitochondria but that it may contribute to cellular damage that culminates in liver failure.
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PMID:The valine catabolic pathway in human liver: effect of cirrhosis on enzyme activities. 893 68