Purification and characterization of phosphoenolpyruvate carboxykinase,a catabolic CO2-fixing enzyme, from Anaerobiospirillum succiniciproducens.

Phosphoenolpyruvate (PEP) carboxykinase (EC 4.1.1.49) from the obligate anaerobe Anaerobiospirillum succiniciproducens was purified 18-fold. The enzyme was monomeric, with an Mr of 57,000 +/- 2,000. The enzyme was oxygen stable, had a pH optimum of 6.7-7.1, and was stable from pH 5.0 to 9.0. The enzyme displayed Michaelis-Menten kinetics for the substrate PEP and the cosubstrates bicarbonate and ADP with a Km of 0.54 mM, 17 mM and 0.42 mM, respectively. The enzyme required Mn(2+) or Co(2+) in addition to Mg(2+) to exhibit maximum activity. p-Chloromercuribenzoate inhibited activity and phosphoenolpyruvate protected the enzyme against inactivation, suggesting that an essential cysteine may be in the active site.