SUMMARY: The requirement of a mutant strain of for lysine + methionine was due to its inability to make lipoic acid. Aerobic growth of the mutant in minimal medium + lipoic acid was equal to that of the wild-type organism. The factor was replaceable by acetate + succinate. When grown without lipoic acid, suspensions of this organism did not oxidize pyruvate but did so upon addition of the factor; they also accumulated pyruvate from glucose. Extracts from deficient organisms did not oxidize α-ketoglutarate with 3-acetyl-NAD as acceptor. The growth requirements were only exhibited aerobically when provision of acetate + succinate required the operation of the lipoic-dependent pyruvate and α-ketoglutarate oxidase systems, respectively. Anaerobically, these metabolites were formed by lipoic-independent mechanisms, such as fumarate reductase which is repressed by oxygen.


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