Bremer J, Davis E J
Biochim Biophys Acta. 1978 Mar 30;528(3):269-75. doi: 10.1016/0005-2760(78)90016-4.
The oxidation of 14C-labelled branched-chain alpha-keto acids corresponding to the branched-chain amino acids valine, isoleucine and leucine has been studied in isolated mitochondria from heart, liver and skeletal muscle. 1. Heart and liver mitochondria have similar capacities to oxidize these alpha-keto acids based on protein content. Skeletal muscle mitochondria also show significant activity. 2. Half maximum rates are obtained with approximately 0.1 mM of the alpha-keto acids under optimal conditions. Added NAD and CoA had no effect on the oxidation rate, showing that endogenous mitochondrial NAD and CoA are required for the oxidation. 3. Addition of carnitine esters of fatty acids (C6--C16), succinate, pyruvate, or alpha-ketoglutarate inhibited the oxidation of the branched chain alpha-keto acids, especially in a high-energy state (no ADP added). In heart mitochondria the addition of AD (low-energy state) decreased the inhibitory effects of acylcarnitines of medium chain length or of pyruvate, and abolished the inhibitory effect of succinate. It is suggested that the oxidation rate is regulated mainly by the redox state of the mitochondria under the conditions used. 4. The results are discussed in relation to the regulation of branched-chain amino acid metabolism in the body.
已对从心脏、肝脏和骨骼肌分离出的线粒体中与支链氨基酸缬氨酸、异亮氨酸和亮氨酸相对应的14C标记的支链α-酮酸的氧化进行了研究。1. 基于蛋白质含量，心脏和肝脏线粒体氧化这些α-酮酸的能力相似。骨骼肌线粒体也表现出显著活性。2. 在最佳条件下，约0.1 mM的α-酮酸可达到最大氧化速率的一半。添加NAD和辅酶A对氧化速率无影响，表明氧化过程需要内源性线粒体NAD和辅酶A。3. 添加脂肪酸的肉碱酯（C6 - C16）、琥珀酸、丙酮酸或α-酮戊二酸可抑制支链α-酮酸的氧化，尤其是在高能状态（未添加ADP）下。在心脏线粒体中添加AD（低能状态）可降低中链长度的酰基肉碱或丙酮酸的抑制作用，并消除琥珀酸的抑制作用。建议在所使用的条件下，氧化速率主要受线粒体的氧化还原状态调节。4. 结合体内支链氨基酸代谢的调节对结果进行了讨论。
