The inhibitory effects of nitrous oxide and methylmercury in vivo on methionine synthase (EC 2.1.1.13) activity in the brain, liver, ovary and spinal cord of the rat.

1. Baseline levels of methionine synthase (MS) activity in spinal cord and ovary from female rats were comparable to activities seen in brain and liver. 2. Exposure (1 hr) of female rats to 50% nitrous oxide (N2O) caused significant decreases in MS in brain, liver, and spinal cord and a sharp drop in ovary. 3. Four daily injections of 6 mg/kg methylmercury (MM) caused a significant decrease in MS activity in brain and a decrease in mean MS activity in ovary and spinal cord. 4. Results from a combined treatment with MM and N2O suggests additive inhibition of MS by these agents.