Arginine metabolism in the sheep abomasal nematode parasites Haemonchus contortus and Teladorsagia circumcincta

The ornithine urea cycle, polyamine synthesis, nitric oxide synthesis and metabolism of arginine to putrescine have been investigated in L3 and adult Haemonchus contortus and Teladorsagia circumcincta. Neither parasite had a detectable arginine deiminase/dihydrolase pathway nor a functional ornithine urea cycle. Nitric oxide synthase was present in central and peripheral nerves, but was not detected in whole parasite homogenates. Both arginase (E.C. 3.5.3.1) and agmatinase (E.C. 3.5.3.11) activities were present in both species. Arginase did not require added Mn²⁺ and had an optimal pH of 8.5. Polyamine metabolism differed in the two species and from that in mammals. Ornithine decarboxylase (E.C. 4.1.1.17) was present in both parasites, but no arginine decarboxylase (E.C. 4.1.1.19) activity was detected in T. circumcincta. The flexibility of synthesis of putrescine in H. contortus may make this pathway less useful as a target for parasite control than in T. circumcincta, in which only the ornithine decarboxylase pathway was detected.