Abstract
Cell-free extracts of a mutant strain of Escherichia coli, W2-3,which required either thiamine or succinate for aerobic growth, and of its parent strain, W, were compared for their ability to catalyze overall oxidation of 2-oxoglutarate. Both extracts catalyzed the reduction of NAD in the presence of 2-oxoglutarate, CoA, and thiamine diphosphate, though the former was less active than the latter. Subsequently, both extracts catalyzed the anaerobic evolution of carbon dioxide from 2-oxoglutarate in the presence of ferricyanide as electron acceptor with variable amounts of thiamine diphosphate. The rate of carbon doixide evolution was always higher in the extracts prepared from the wild type strain than those prepared from the mutant strain at the same concentration of thiamine diphosphate. These results suggest that the biochemical lesion which was altered genetically in the mutant strain was at a stage in the decarboxylation of 2-oxoglutarate and that the stage was not blocked completely but the enzymic properties might be changed and became to require thiamine diphosphate in excess.
