The control of the synthesis of pyruvate carboxylase in Pseudomonas citronellolis. Evience from double labeling studies

The level of pyruvate carboxylase in Pseudmonas citronellolis is controlled by the carbon source of the growth medium. The activity of the enzyme is highest in cells grown on lactate or glucose and virtually absent in cells grown on malate or aspartate. Double labeling studies with 3H- and 14C-labeled leucine confirm that pyruvate carboxylase is synthesized in the presence of lactate but not in the presence of aspartate. The studies also show that coordinated regulation occurs at the level of the synthesis of the two polypeptides which make up pyruvate carboxylase in P. citronellolis, rather than at the stages of their assembly into protomers or the biotinylation of the apoenzyme. There is no evidence for control of the catalytic acitivity of the holoenzyme via effectors. In all other varieties of pyruvate carboxylase examined thus far, the enzyme appears to be constitutive with regulation accomplished either through effector modulation of holoenzyme activity (pyruvate carbox-lase from animal sources, yeast, several species of bacteria) or through control of the biotinylation of the apoenzyme by holocarboxylase synthetase (Bacillus stearothermophilus, yeast).