A systematic analysis of the structure, function, and regulation of the pyruvate and alpha-ketoglutarate dehydrogenase complexes from microorganisms and from mammalian tissues is continuing. The pyruvate and alpha-ketoglutarate dehydrogenase complexes contain a core, consisting of dihydrolipoyl transacetylase or dihydrolipoyl transsuccinylase, to which pyruvate dehydrogenase or alpha-ketoglutarate dehydrogenase and dihydrolipoyl dehydrogenase are joined by noncovalent bonds. The mammalian pyruvate dehydrogenase complex contains, in addition to the three catalytic enzymes, two regulatory enzymes - a kinase and a phosphatase. Characterization of the purified kinase is in progress. Experiments are also in progress to gain further understanding of the physiological regulation of the activity of the kinase and the phosphatase. Systematic studies will be conducted on the stoichiometry of binding and binding constants of the component enzymes of the Escherichia coli pyruvate and alpha-ketoglutarate dehydrogenase complexes.