Kinetic properties of glutamate metabolism in the nematode parasite Haemonchus contortus (L3)

Abstract

The key steps in cell metabolism of all organisms are the synthesis of both glutamate and glutamine because they denote the only means of incorporating inorganic nitrogen into carbon backbones. In this study, an assay for the activity of two key enzymes in nitrogen metabolisms such as glutamate dehydrogenase (GDH) and glutamine synthase (GOGAT) was conducted using homogenates of L₃ larvae of Haemonchus contortus. GDH was assayed both in the direction of glutamate utilisation and glutamate formation. GOGAT activity was monitored in the direction of glutamine utilisation. The present result showed that H.contortus had a high K_m for ammonia (27.22mM) and glutamine (15.04 mM). The high K_m for ammonia suggests a very low affinity for ammonia, meaning that in the reversible amination of 2-oxoglutarate to glutamate, the predominant direction is likely to be glutamate deamination and not the incorporation of ammonia. The activity of GOGAT was also demonstrated but with a high K_m, which indicates a low binding affinity of glutamine to the enzyme. Nevertheless, the presence of the two key enzymes of nitrogen metabolism, i.e. GDH and GOGAT, may provide a potential target for anthelmintic action.