期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1978
卷号：75
期号：10
页码：4881-4885
DOI：10.1073/pnas.75.10.4881
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：A branched chain -keto acid dehydrogenase-dihydrolipoyl transacylase complex was purified to apparent homogeneity from bovine kidney mitochondria. As usually isolated, the complex (s20,w = 40 S) contained little, if any, dihydrolipoyl dehydrogenase. When saturated with the latter enzyme the complex had a specific activity of about 12 {micro}mol of -ketoisovalerate oxidized per min per mg of protein at 30{degrees} with NAD+ as electron acceptor. In addition to -ketoisovalerate, the complex also oxidized -ketoisocaproate, -keto-{beta}-methylvalerate, -ketobutyrate, and pyruvate. The ratios of the specific activities were 2.0:1.5:1.0:1.0:0.4, and the apparent Km values were 40, 50, 37, 56, and 1000 {micro}M. The complex was separated into its component enzymes. The branched chain -keto acid dehydrogenase (6 S) consists of two different subunits with estimated molecular weights of 46,000 and 35,000. The dihydrolipoyl transacylase (20 S) contains apparently identical subunits of molecular weight about 52,000. In the electron microscope, the transacylase has the appearance of a cube, and the molecules of branched chain -keto acid dehydrogenase appear to be distributed on the surface of the cube. In contrast to the pyruvate dehydrogenase complex of bovine kidney, the branched chain -keto acid dehydrogenase complex apparently is not regulated by phosphorylation-dephosphorylation. Its activity, however, is subject to modulation by end-product inhibition.
