Control of the Synthesis of Phosphoenolpyruvate Carboxylase and Phosphoenolpyruvate Carboxykinase in Escherichia coli*

Abstract

The level of phosphoenolpyruvate (PEP) carboxylase (EC 4. 1. 1. 31) in Escherichia coli W was remarkably affected by the carbon source in the growth medium. The enzyme level was found to decrease in the following order: glucose>glycerol>malate>lactatc>acetate>aspartate. Several lines of evidence support that PEP carboxylase is nutritionally induced by glucose bur not repressed by any compound related to the tricarboxylic acid cycle. The level of PEP carboxykinase [EG 4. 1. 1. 49] in-the cells grown on malate-, aspartate-, or enriched media was 4- to 7-fold higher than that on glucose media. The synthesis of PEP carboxykinase was presumed to be nutritionally repressed by glucose. In view of the antagonistic behaviors of these two enzymes in the cells grown on various carbon sources, the syntheses of both enzymes seem to be inversely regulated each other. The regulatory mechanism concerned in the syntheses of these two physiologically antagonistic enzymes was supposed to play an important role in the metabolic shift from glycolysis to gluconeogenesis, or vice versa.