Activities of α-ketoisovalerate, pyruvate, and α-ketoglutarate dehydrogenases in a mutant of Bacillus subtilis

An acetate-requiring leaky mutant was induced from Bacillus subtilis 168, and activities of its three α-keto acid dehydrogenases were compared with the respective activities of the parent strain. Both pyruvate and α-ketoisovalerate dehydrogenase activities in the mutant were considerably lower, being only 10–17% of those of the parent, but α-ketoglutarate dehydrogenase activity was unchanged. These dehydrogenases are complexes composed of three enzymes: a carboxylase, a lipoic reductase–transacylase, and a dihydrolipoyl dehydrogenase. The carboxylase activity of the affected complexes was no different. Total dihydrolipoyl dehydrogenase activity was only one-third. Thus dihydrolipoyl dehydrogenase is the defective enzyme in the two dehydrogenase complexes; the activity remaining in the mutant is accounted for by the activity of the intact α-ketoglutarate dehydrogenase.