Wild-type and mutant forms of the pyruvate dehydrogenase multienzyme complex from Bacillus subtilis

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Abstract
A simple procedure is described for the purification of the pyruvate dehydrogenase complex and dihydrolipoamide dehydrogenase from B. subtilis. The method is rapid and applicable to small quantities of bacterial cells. The purified pyruvate dehydrogenase complex comprises multiple copies of 4 different types of polypeptide chain, with apparent MW values of 59,500, 55,000, 42,500 and 36,000; these were identified as the polypeptide chains of the lipoate acetyltransferase (E2), dihydrolipoamide dehydrogenase (E3) and the 2 types of subunit of the pyruvate decarboxylase (E1) components, respectively. Pyruvate dehydrogenase complexes were also purified from 2 ace (acetate-requiring) mutants of B. subtilis. That from mutant 61142 is inactive, owing to an inactive E1 component, which was bound less tightly than wild-type E1 and was graudally lost from the E2E3 subcomplex during purification. Subunit-exchange experiments demonstrated that the E2E3 subcomplex retained full enzymic activity, suggesting that the lesion was limited to the E1 component. Mutant 61141R elaborated a functional pyruvate dehydrogenase complex, but this also contained a defective E1 component, the Km for pyruvate being raised from 0.4-4.3 mM. The E1 component rapidly dissociated from the E2E3 subcomplex at low temperature (0.degree.-4.degree. C), leaving an E2E3 subcomplex which by subunit exchange experiments was judged to retain full enzyme activity. These ace mutants provide interesting opportunities to analyze defects in the self-assembly and catalytic activity of the pyruvate dehydrogenase complex.

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