Brief Report: Lack of Effect of L-Methionine Ingestion on 14CO2 Excretion from L-Histidine (Imidazole-2-14C) in Folic Acid and Vitamin B12 Deficient Humans

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Abstract
Three human subjects with folic acid and one with vitamin B12 deficiency failed to show any effect of ingestion of L-methionine (400-800 µg./kg. body weight) on the production of 14CO2 from parenterally administered high specific activity L-histidine (imidazole-2-14C). It is suggested that the inhibitory effect of methionine on intestinal absorption and cell membrane transport of histidine can explain previously published effects of methionine on the oxidation of the imidazole-2 carbon atom of L-histidine and that a direct effect of methionine on histidine metabolism need not be invoked.