Regulation of Escherichia Coli Phosphoenolpyruvate Carboxylase by Multiple Effectors in Vivo. Estimation of the Activities in the Cells Grown on Various Compounds

Intracellular concentrations of phosphoenolpyruvate (PEP) and five kinds of allosteric effectors (acetyl-CoA, fructose 1,6-bisphosphate, GTP, L-aspartate, and L-malate) of PEP carboxylase were measured in E. coli cells grown on various compounds as a carbon source. Based on the data obtained, reaction systems which contained a definite concentration of the enzyme and the ligands at the concentrations found in vivo were constructed and the enzyme activities were measured. The ratio of each activity thus obtained to the maximal activity attainable with the same concentration of enzyme and saturating concentrations of the activators was estimated. For the cells grown on glucose, glycerol, or lactate, the extent of exhibition of the enzyme activity was 2-15% of the maximal activity. For the cells grown on acetate or oleate, the extent was 1-3%. For the cells grown on succinate, L-aspartate, L-malate, or glucose plus L-aspartate, the extent was less than 0.4%. Consideration of the data obtained in the present studies, together with those obtained in our previous studies on the enzyme level (Teraoka, H. et al. (1970) J. Biochem. 67, 567-575), showed that the control of the enzyme reaction in vivo is considerably different from that expected from the in vitro experiments, and that deficiencies of "coarse control" are covered by a "fine control."