Abstract
Malate dehydrogenase (MDH) was partially purified from bovine heart and rumen epithelium. Electrophoretic mobility of MDH from crude extracts of bovine heart, muscle, liver, kidney, brain and rumen epithelium revealed two bands of enzyme activity which were indistinguishable among tissues. The partially purified MDHs aligned with the slow moving isozyme in the crude extracts which was subsequently found to be the mitochondrial form of the enzyme. The pH and temperature optima and apparent Km's for both the heart and epithelial enzymes were similar. MDH activity, measured as NAD reduction, was inhibited 9–30% by 1 mM AMP, ADP and ATP. Acetate and volatile fatty acyl-CoA salts also inhibited the rate of NAD reduction. Combinations of volatile fatty acids and ATP or ADP appeared to be additive. Acetate also stimulated the activity of "malic" enzyme from rumen epithelium while propionate and propionyl-CoA did not. The implications of a "malic" enzyme-MDH control mechanism which may be required for NADPH production is discussed. Key words: Malate dehydrogenase, bovine, heart, rumen epithelium
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