Zhao Y, Popov K M, Shimomura Y, Kedishvili N Y, Jaskiewicz J, Kuntz M J, Kain J, Zhang B, Harris R A
Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis 46202-5122.
Arch Biochem Biophys. 1994 Feb 1;308(2):446-53. doi: 10.1006/abbi.1994.1063.
Levels of expression of two subunits of the liver branched-chain alpha-ketoacid dehydrogenase complex in response to extremes of dietary protein intake (50% versus 0% protein diet) were determined by quantitative immunoblotting. Dietary protein deficiency decreased the amount of E1 alpha protein to a greater extent than E2 protein. The ratio of E1 alpha to E2 was below 1 in the liver of animals starved for protein and above 1 in the liver of animals fed the high-protein diet. Supplementation of the 0% protein diet with 5% leucine (but not 5% valine) had the same effect as the 50% protein diet. The extremes of dietary protein also resulted in a divergent pattern of expression of the mRNAs for the subunits of the complex. The E1 beta message showed the expected corollary of being greater in the liver of the high-protein-fed rats than the no-protein-fed rats. In contrast, the E2 message was not affected by the two extremes of dietary protein and the E1 alpha message was greater in the liver of the no-protein-fed rats than the high-protein-fed rats. Thus, coordinate regulation of gene expression of the subunits of the complex does not occur in response to dietary protein. Post-transcriptional regulatory mechanisms most likely determine the amount of the complex and the ratio of its subunits. The decrease in E1 alpha/E2 protein ratio that occurs in dietary protein deficiency may increase sensitivity of the complex to phosphorylation-mediated inhibition by branched-chain alpha-ketoacid dehydrogenase kinase.
通过定量免疫印迹法测定了肝脏支链α-酮酸脱氢酶复合体两个亚基在极端饮食蛋白质摄入量（50%蛋白质饮食与0%蛋白质饮食）情况下的表达水平。饮食蛋白质缺乏使E1α蛋白量的减少程度大于E2蛋白。在蛋白质饥饿动物的肝脏中，E1α与E2的比值低于1，而在高蛋白饮食动物的肝脏中则高于1。用5%亮氨酸（而非5%缬氨酸）补充0%蛋白质饮食产生的效果与50%蛋白质饮食相同。极端的饮食蛋白质情况还导致该复合体亚基的mRNA表达模式出现差异。E1β信息显示出预期的结果，即在高蛋白喂养大鼠的肝脏中比无蛋白喂养大鼠的肝脏中更多。相反，E2信息不受两种极端饮食蛋白质情况的影响，而E1α信息在无蛋白喂养大鼠的肝脏中比高蛋白喂养大鼠的肝脏中更多。因此，复合体亚基的基因表达不会因饮食蛋白质而发生协同调节。转录后调节机制很可能决定了复合体的量及其亚基的比例。饮食蛋白质缺乏时出现的E1α/E2蛋白比值下降可能会增加该复合体对支链α-酮酸脱氢酶激酶磷酸化介导抑制的敏感性。
