The Effect of Nitrous Oxide‐Induced Inactivation of Cobalamin on Plasma Amino Acid Levels in the Rat

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Abstract
Rats were maintained in an atmosphere of equal volumes of O2/N2O (1/1) for up to 7 days and plasma levels of Met, Gly, Ser, His, homocysteine and S-methylcysteine were measured. There was a fall in plasma Met and a rise in plasma Ser levels. There were no significant changes in Gly and His levels. Homocysteine and S-methylcysteine were not detected in rat plasmas. The fall in plasma Met was due to loss of cobalamin-dependent methionine synthetase activity. The rise in plasma Ser may be due to decline in its metabolism via methenyltetrahydrofolate cyclohydrolase which was concerned in oxidizing the methenyl-Ca (.dbd.CH.sbd.), initially derived as a methylene-Ca (.sbd.CH2.sbd.) from Ser to formate (.sbd.CHO).