Abstract
A mutant strain of Escherichia coli 70-23,which requires thiamine as the intact molecule, was able to grow on succinate under anaerobic conditions, and a minute amount of thiamine pyrophosphate was found in the cells grown on succinate. Aerobically, this mutant did not respond appreciably to the substance. The different responses under aerobic and anaerobic conditions suggested that the mutant could synthesize thiamine in a limited amount under the conditions in which excess succinate was present intracellularly. It was already pointed out that the biochemical lesion in the mutant strain was in the phosphorylating step of pyrimidine moiety of thiamine. Such a blocked reaction, therefore, would be relieved to some extent by the presence of excess amounts of succinate. Subsequently, the abilities of both mutant and wildtype cells to oxidize pyruvate were measured. The results showed that pyruvate markedly stimulated the respiration of the mutant cells grown on thiamine or of the wild-type cells grown on succinate. The addition of external thiamine into the reaction mixture did not cause the further stimulation. On the other hand, in the case of the mutant cells grown on succinate the degree of pyruvate oxidizing activity was very low but the activity was fully restored by the addition of thiamine. These and other nutritional experiments led to the conclusion that the mutant cells grown on succinate under anaerobic conditions were deficient in thiamine.
