Metabolic regulation of pyruvate kinase isolated from autotrophically and heterotrophically grown Paracoccus denitrificans.

Pyruvate kinase (ATP: pyruvate phosphotransferase (EC 2.7.1.40) was partially purified from both autotrophically and heterotrophically grown Paracoccus denitrificans. The organism grown under heterotrophic conditions contains four times more pyruvate kinase than under autotrophic conditions. The enzyme isolated from both sources exhibited sigmoidal kinetics for both phosphoenolpyruvate (PEP) and ADP. The apparent Km for ADP and PEP in the "autotrophic" enzyme were 0.63 mM ADP and 0.25 mM PEP. The effect of several low molecular weight metabolites on the pyruvate kinase activity was investigated. Ribose-5-phosphate, glucose-6-phosphate and AMP stimulated the reaction at low ADP levels; this stimulation was brought about by an alteration in the apparent Km for ADP. The pyruvate kinases differ in their response to adenine nucleotides, but both preparations seem to be under adenylate control. The results are discussed in relation to the role of pyruvate kinase as a regulatory enzyme in P. denitrificans grown under both autotrophic and heterotrophic conditions.