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Regulation of leucine catabolism mechanism responsible for oxidizable substrate inhibition and di chloro acetate stimulation of leucine oxidation by the heart


, : Regulation of leucine catabolism mechanism responsible for oxidizable substrate inhibition and di chloro acetate stimulation of leucine oxidation by the heart. Archives of Biochemistry & Biophysics 200(2): 336-345

In the absence of any other oxidizable substrate, the perfused rat heart oxidizes [1-14C]-leucine to 14CO2 at a rapid rate and releases only small amounts of .alpha.[1-14C]ketoisocaproate into the perfusion medium. The branched-chain .alpha.-keto acid dehydrogenase complex, assayed in extracts of mitochondria prepared from such perfused hearts, is very active. Under such perfusion conditions, dichloroacetate has almost no effect on [1-14C]leucine oxidation, .alpha.-[1-14C]ketoisocaproate release, or branched-chain .alpha.-keto acid dehydrogenase activity. Perfusion of the heart with some other oxidizable substrate, i.e., glcuose, pyruvate, ketone bodies, or palmitate, results in an inhibition of [1-14C]leucine oxidation to 14CO2 and the release of large amounts of .alpha.-[1-14C]ketoisocaproate into the perfusion medium. The branched-chain .alpha.-keto acid dehydrogenase complex, assayed in extracts of mitochondria prepared from such hearts, is almost completely inactivated. The enzyme can be reactivated by incubating the mitochondria at 30.degree. C without an oxidizable substrate. With hearts perfused with glucose or ketone bodies, dichloroacetate greatly increases [1-14C]leucine oxidation, decreases .alpha.-[1-14C]ketoisocaproate release into the perfusion medium, and activates the branched-chain .alpha.-keto acid dehydrogenase complex. Pyruvate may block dichloroacetate uptake because dichloroacetate neither stimulates [1-14C]leucine oxidation nor activates the branched-chain .alpha.-keto acid dehydrogenase complex of pyruvate-perfused hearts. Leucine oxidation by heart may be regulated by the activity of the branched-chain .alpha.-keto acid dehydrogenase complex which is subject to interconversion between active and inactive forms. Oxidizable substrates establish conditions which inactivate the enzyme. Dichloroacetate, known to activate the pyruvate dehydrogenase complex by inhibition of pyruvate dehydrogenase kinase, causes activation of the branched-chain .alpha.-keto acid dehydrogenase complex, suggesting the existence of a kinase for this complex.

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