THIOREDOXIN REDUCTION DEPENDENT ON ALPHA-KETOACID OXIDATION BY ALPHA-KETOACID DEHYDROGENASE COMPLEXES

The pyruvate and alpha-ketoglutarate dehydrogenase complexes isolated from pig heart mitochondria promote the reduction of thioredoxin in th e presence of their alpha-ketoacid substrates, coenzyme A, and free li poate. Substrate-specific generation of reduced thioredoxin was establ ished by two independent methods, viz. reduction of insulin and thiore doxin reductase-catalyzed NADPH formation. Dihydrolipoate accumulating in the absence of NAD+ is the likely intermediate. A redox function i n alpha-ketoacid oxidation provides a potential role for the specific thioredoxins previously identified by us in mitochondria.