Purification and properties of phosphoenolpyruvate carboxykinase from Hymenolepis diminuta (Cestoda).

A method is described for the purification of the enzyme phosphoenolpyruvate carboxykinase (PEPCK) from the cestode Hymenolepis diminuta. When purified to electrophoretic homogeneity, the enzyme had a molecular weight of 70,600 and an isoelectric point of 7.5. Kinetic studies indicated that the pH 5.6 was optimal for the carboxylation reaction and that Mn++ was the preferred divalent cation; there was no activity of the enzyme in the presence of Mg++. Apparent Km values for the carboxylation reaction were determined; those for GDP (20.6 muM) and PEP (38.9 muM) were lower than the values previously reported. GTP, GMP, ITP, IMP, fumarate, succinate and alpha-ketoglutarate were found to be competitive inhibitors and their Ki values determined.