Biological significance of phosphoenolpyruvate carboxykinase in a cestode parasite, Raillietina echinobothrida and effect of phytoestrogens on the enzyme from the parasite and its host, Gallus domesticus

摘要

Phosphoenolpyruvate carboxykinase ( PEPCK) is involved in glycolysis in the cestode parasite, Raillietina echinobothrida; whereas, it executes a gluconeogenic role in its host, Gallus domesticus. Because of its differing primary function in the cestode parasite and its host, this enzyme is regarded as a plausible anthelmintic target. Hence, the biological significance of PEPCK in the parasite was analysed using siRNA against PEPCK from R. echinobothrida ( RePEPCK). In order to find out the functional differences between RePEPCK and GdPEPCK ( PEPCK from its host, G. domesticus), PEPCK genes from both sources were cloned, over-expressed, characterized, and some properties of the purified enzymes were compared. RePEPCK and GdPEPCK showed a standard Michaelis-Menten kinetics with K-mapp of 46.9 and 22.9 mu M, respectively, for phosphoenolpyruvate and K-mapp of 15.4 mu M for oxaloacetate in GdPEPCK decarboxylation reaction. Here, we report antagonist behaviours of recombinant PEPCKs derived from the parasite and its host. In search of possible modulators for PEPCK, few phytoestrogens were examined on the purified enzymes and their inhibitory constants were determined and discussed. This study stresses the potential of these findings to validate PEPCK as the anthelmintic drug target for parasitism management.