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

An acetate-requiring leaky mutant was induced from Bacillus subtilis 168, and activities of its three alpha-keto acid dehydrogenases were compared with the respectives activities of the parent strain. Both pyruvate and alpha-ketoisovalerate dehydrogenase activities in the mutant were consideralby lower, being only 10-17% of those of the parent, but alpha-ketoglutarate dehydrogenase activity was unchanged. These dehydrogenases are complexed 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 alpha-ketoglutarate dehydrogenase.