α-Keto acid dehydrogenase complexes

The Escherichia coli Crookes pyruvate dehydrogenase complex contains a core, consisting of dihydrolipoyl transacetylase, to which pyruvate dehydrogenase and dihydrolipoyl dehydrogenase (a flavoprotein) are joined by noncovalent bonds. Electron microscopic studies indicated that the design of the transacetylase is based on octahedral (432) symmetry and, therefore, it would be expected to contain 24 very similar, if not identical, polypeptide chains. Evidence is presented that the transacetylase does indeed consist of 24 apparently identical polypeptide chains. Each dehydrogenase (about 112,000). Both the uncomplexed pyruvate dehydrogenase and the flavoprotein contain two apparently identical polypeptide chains. The available data do not permit a decision as to whether each of these enzymes is present in the complex as a monomer or a dimer. It appears that the E. coli Crookes pyruvate dehydrogenase complex contains 24 pyruvate dehydrogenase chains, 24 dihydrolipoyl transacetylase chains, and 12 flavoprotein chains. Possible distributions of the pyruvate dehydrogenase chains and the flavoprotein chains around the transacetylase core are discussed.