Summary
The effect of butyl and isoamyl nitrites on methionine synthase from mouse kidney and liver was investigated. A strong specific inhibition of the enzyme (50% at 7.3 x 10 4 M nitrites for kidney methionine synthase) was found. This inhibition was caused mainly by the destruction of vitamin B12 as shown in experiments with and without exogenous vitamin B12 in the reaction mixture although decomposition of 5-methyltetrahydrofolate could not be excluded. When given to the mice nitrites did not inhibit methionine synthase, but caused oxidation of hemoglobin to methemoglobin. Alkyl nitrites cannot, therefore, be used to evoke vitamin B12 and folate deficiency in vivo.
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