Glutamate synthase, but not GABA shunt enzymes, contributes to nitrogen metabolism of the sheep abomasal nematode parasites Haemonchus contortus and Teladorsagia circumcincta

Glutamate synthase (E.C. 1.4.1.14) (GOGAT) activity was not detectable in L3 Haemonchus contortus, but was present in L3 Teladorsagia circumcincta and adult worms of both species. GOGAT activity was inhibited by 80% by azaserine. Activity (nmol min−1 mg−1 protein) was 33–59 in adult H. contortus, 51–91 in adult T. circumcincta and 24–41 in L3 T. circumcincta, probably depending on exposure to ammonia, as incubation with 1 mM NH4Cl doubled GOGAT activity. The pH optimum was 7.5 in both species. Either NAD or NADP acted as co-factor. The mean apparent Km for 2-oxoglutarate was 0.7 (0.5–0.9) mM and for glutamine was 1.0 (0.5–1.7) mM for different homogenates. There was no detectable activity in whole parasite homogenates of glutamate decarboxylase (E.C. 4.1.1.15) or succinic semialdehyde dehydrogenase (E.C. 1.2.1.24), the first and third enzymes of the GABA shunt, respectively, suggesting that the GABA shunt is not important in general metabolism in these species.

Figure optionsDownload as PowerPoint slideResearch highlights
► Glutamate synthase (GOGAT) activity in adult H. contortus and T. circumcincta.
► GOGAT activity in L3 T. circumcincta but not H. contortus.
► Exposure to ammonia increases GOGAT activity.
► GABA shunt appears to be unimportant for nitrogen metabolism in abomasal nematodes.
► Abomasal nematodes capable of assimilating ammonia into amino acids.