Control of the Carbon Dioxide Fixation in Escherichia coli by the Compounds Related to TCA Cycle*

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Abstract
1. It was demonstrated by using 14C-bicarbonate that the CO2 fixation to the cell material was depressed by the addition of aspartate to the Escherichia coli W culture growing on the glucose-salts medium. This phenomenon was found neither due to the dilution of 14CO2 nor due to that of 14C-aspartate synthesized. 2. With cell-red extracts of this organism, a more remarkable fixation of CO2 was observed with phosphoenolpyruvate than with pyruvate. The evidence obtained suggested the involvement of phosphoenol-pyruvate carboxylase [EC 4. 1. 1. 31] in the reaction. The reaction was activated by acetyl-CoA, or by CoA and acetyl phosphate. 3. The effect of various compounds on the CO2-fixation reaction was investigated in cell-free extracts. It was found that L-aspartate, L-malate and fumarate strongly inhibited this reaction. The inhibition by L-aspartate was observed also with a partially purified phosphoenolpyruvate carboxylase. 4. The physiological significance of the inhibitory effect of these compounds in the growing cells was discussed from the standpoint of the control of aspartate biosynthesis and of oxaloacetate production for the maintenance of the tricarboxylic acid cycle.