Purification and characterization of phosphoenolpyruvate carboxykinase fromRaillietina echinobothrida, a cestode parasite of the domestic fowl

Abstract

SUMMARYPhosphoenolpyruvate carboxykinase (PEPCK, EC 4.1.1.32) is an essential regulatory enzyme of glycolysis in helminths in contrast to its role in gluconeogenesis in their host. Previously we have reported that phytochemicals fromFlemingia vestita(Family: Fabaceae), genistein in particular, have vermifugal action and are known to affect carbohydrate metabolism in the cestode,Raillietina echinobothrida. In order to determine the functional differences of PEPCK from the parasite and its avian host (Gallus domesticus), we purified the parasite enzyme apparently to homogeneity, and characterized it. The native PEPCK is a monomer with a subunit molecular weight of 65 kDa. The purified enzyme displayed standard Michaelis-Menten kinetics withKm value of 42·52μM for its substrate PEP. TheKi for the competitive inhibitors GTP, GMP, ITP and IMP for the carboxylation reaction were determined and discussed. In order to identify putative modulators from plant sources, phytochemicals fromF. vestitaandStephania glabrawere tested on the purified PEPCK, which resulted in alteration of its activity. From our results, we hypothesize that PEPCK may be a potential target site for anthelmintic action.