Phosphoenolpyruvate carboxylase in the carboyxdobacterium, Pseudomonas gazotropha

The activity of phosphoenolpyruvate carboxylase (orthophosphate: oxalacetate-carboxy-lyase phosphorylating, E. C. 4.1.1.31) in the cell extracts of the carboxydobacterium Pseudomonas gazotropha Z-1156 depends on the presence of bivalent metal ions, Mn2+ ions being more effective than Mg2+ ions. The value of apparent KM for phosphoenolpyruvate in a freshly prepared extract is 7.1 mM. The affinity of the enzyme to phosphoenolpyruvate increases after storage of the extract in ice in the presence of dithiothreitol: KM=0.42 mM at low concentrations of the substrate, and 2.5 mm, at high concentrations of the substrate. The calculated maximum rate is 18.1 mE per 1 mg of protein of the extract, and changes only slightly upon storage in the presence of a stabilizer of sulphydryl groups. The activity of the enzyme reaches its maximum at the phase of deceleration of growth. Nucleotide triphosphates inhibit the activity of the enzyme more than the corresponding nucleotide diphosphates. The properties of PEP-carboxylase are discussed from the viewpoint of comparative biochemistry.