Dissociation of methionine synthetase (EC 2.1.1.13) activity and impairment of DNA synthesis in fruit bats (Rousettus aegyptiacus) with nitrous oxide-induced vitamin B12 deficiency

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Abstract
1. The effect of methylcobalamin inactivation by the anaesthetic gas nitrous oxide on the activity of the cobalamin-dependent methionine synthetase (5-methyltetrahydrofolate homocysteine methyltransferase; EC 2.1. I. 13) reaction, and on DNA synthesis, in the fruit bat Rousettus aegyptiucus, was examined.2. Methionine synthetase activity in the liver of bats exposed to N2O—oxygen (50: 50, v/v) for 90 min/d averaged 32% of that of controls after 4 d of exposure and only 5% after 12–14 weeks of exposure.3. DNA synthesis in the bone marrow, as reflected by the deoxyuridine suppression test, was unaffected by 4 d of exposure to N2O and only minimally affected after 5–10 weeks of exposure.4. These results suggest that DNA synthesis in the fruit bat is unusually resistant to inhibition of methionine synthetase and imply the existence of a non-methylated circulating folate pool in this species.