Activity of N-acetylglucosamine-1-phosphate transferase in sheep liver microsomes: in vivo and in vitro inhibition by tunicamycin.

The neurological disease of livestock known as annual ryegrass toxicity, caused by ingestion of bacterial toxins called corynetoxins, has been shown to be produced experimentally by injection of tunicamycin, a related antibiotic. In this study the effects of tunicamycin inhibition on the activity of the enzyme, N-acetylglucosamine-1-phosphate transferase, in sheep liver rough microsomes were measured in vitro and in vivo. Enzyme activity was dependent on Triton X-100 and exogenous dolichyl phosphate for maximal activity, although there was measurable activity in their absence. The transferase enzyme was very sensitive to in vitro (inhibition can be detected below 10 ng ml(-1)). In vivo, sheep treated parenterally with a single dose of tunicamycin showed a time and dose-dependent decrease in enzyme activity, which was almost completely inhibited for up to 14 days after a sublethal dose of toxin. In addition, the yield of rough microsomes was lower from toxin-treated sheep than from control animals.