Studies on the regulation of leucine catabolism. Mechanism responsible for oxidizable substrate inhibition and dichloroacetate stimulation of leucine oxidation by the heart.
Studies on the regulation of leucine catabolism. Mechanism responsible for oxidizable substrate inhibition and dichloroacetate stimulation of leucine oxidation by the heart.
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亮氨酸分解代谢调节的研究。
DOI：
10.1016/0003-9861(80)90363-x
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发表时间：
1980
影响因子：
3.9
通讯作者：
Harris,RA
中科院分区：
文献类型：
--
作者：
Sans,RM;Jolly,WW;Harris,RA
在没有任何其他可氧化底物的情况下，灌流的大鼠心脏迅速将[1-14C]亮氨酸氧化为14CO2，并仅向灌流介质中释放少量的α-[1-14C]酮基异己酸。从这种灌流的心脏制备的线粒体提取液中检测到的支链α-酮酸脱氢酶复合体非常活跃。在此灌流条件下，二氯乙酸酯对[1-14C]亮氨酸氧化、α-[1-14C]酮异戊酸释放或支链α-酮酸脱氢酶活性几乎没有影响。心脏灌流一些其他可氧化的底物，例如葡萄糖、丙酮酸、酮体或棕榈酸酯，结果是抑制[1-14C]亮氨酸氧化为14CO2，并将大量α-[1-14C]酮基异己酸酯释放到灌流介质中。从这类心脏制备的线粒体提取液中检测到的支链α-酮酸脱氢酶复合体几乎完全失活。然而，这种酶可以通过在30°C的温度下孵育线粒体而重新激活，而不需要氧化的底物。当心脏灌流葡萄糖或酮体时，二氯乙酸酯显著增加[1-14C]亮氨酸的氧化，减少α-[1-14C]酮异戊酸向灌流介质的释放，并激活支链α-酮酸脱氢酶复合体。丙酮酸可能阻止二氯乙酸酯的摄取，因为二氯乙酸酯既不刺激[1-14C]亮氨酸氧化，也不激活丙酮酸灌流心脏的支链α-酮酸脱氢酶复合体。这表明心脏对亮氨酸的氧化受支链α-酮酸脱氢酶复合体的活性调节，该复合体经历了活性和非活性形式之间的相互转换。可氧化的底物建立了使酶失活的条件。已知的二氯乙酸酯通过抑制丙酮酸脱氢酶激酶来激活丙酮酸脱氢酶复合体，导致支链α-酮酸脱氢酶复合体的激活，这表明该复合体存在一个激酶。
In the absence of any other oxidizable substrate, the perfused rat heart oxidizes [1-14C]leucine to14CO2at a rapid rate and releases only small amounts of α-[1-14C]ketoisocaproate into the perfusion medium. The branched-chain α-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, α-[1-14C]ketoisocaproate release, or branched-chain α-keto acid dehydrogenase activity. Perfusion of the heart with some other oxidizable substrate, e.g., glucose, pyruvate, ketone bodies, or palmitate, results in an inhibition of [1-14C]leucine oxidation to14CO2and the release of large amounts of α-[1-14C]ketoisocaproate into the perfusion medium. The branched-chain α-keto acid dehydrogenase complex, assayed in extracts of mitochondria prepared from such hearts, is almost completely inactivated. The enzyme can be reactivated, however, by incubating the mitochondria at 30 °C without an oxidizable substrate. With hearts perfused with glucose or ketone bodies, dichloroacetate greatly increases [1-14C]leucine oxidation, decreases α-[1-14C]ketoisocaproate release into the perfusion medium, and activates the branched-chain α-keto acid dehydrogenase complex. Pyruvate may block dichloroacetate uptake because dichloroacetate neither stimulates [1-14C]leucine oxidation nor activates the branched-chain α-keto acid dehydrogenase complex of pyruvate-perfused hearts. It is suggested that leucine oxidation by heart is regulated by the activity of the branched-chain α-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 α-keto acid dehydrogenase complex, suggesting the existence of a kinase for this complex.