Subunit structure of dihydrolipoamide acetyltransferase component of pyruvate dehydrogenase complex from bovine kidney.

The pyruvate dehydrogenase complex has been isolated from bovine kidney mitochondria under special anti-proteolytic conditions yielding preparations with a specific activity of up to 20 U/mg protein. Dihydrolipoamide acetyltransferase resolved from the complex was subjected to limited proteolysis resulting in the formation of two major fragments with apparent molecular weights of 36000 and 28000. The fragments were isolated by extraction from dodecyl sulfate polyacrylamide gels and were both shown to possess enzymatic activity for acetyl transfer. Acetylation studies indicated that each fragment contains one protein-bound lipoyl group. It is concluded that the kidney dihydrolipoamide acetyltransferase subunit consists of two homologous if not identical domains. A model is suggested where the acetyltransferase core of the mammalian pyruvate dehydrogenase complex is made up of 30 polypeptide chains whose 60 domains could be arranged in pentagonal dodecahedron symmetry quite similar as proposed for the 60 subunit structure of the acetyltransferase core.