Identification of specific subunits of highly purified bovine liver branched-chain ketoacid dehydrogenase

Publisher Website
Google Scholar
Abstract
Branched-chain .alpha.-ketoacid dehydrogenase was purified to homogeneity from bovine liver mitochondria. The isolated complex has a specific activity of 5-8 .mu.mol of NADH min-1 (mg of protein)-1 as isolated and does not require the addition of exogenous lipoamide dehydrogenase for activity. Addition of porcine heart lipoamide dehydrogenase stimulated complex activity by no more than 20%. Four subunits copurify with the complex with MW by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of 55,000, 52,000, 46,500 and 37,500. The 52,000-dalton subunit is the lipoyl-containing transacylase component of the complex. The branched-chain ketoacid dehydrogenase complex is probably physically and catalytically similar to, but separate from, the pyruvate and .alpha.-ketoglutarate dehydrogenase complexes. The transacylase of the branched-chain ketoacid dehydrogenase complex has an exposed trypsin-sensitive region. Proteolytic action of trypsin separates a lipoyl-containing component from the remainder of the protein. Data presented here and elsewhere definite a specific function for 3 of the 4 subunits.