Inhibition of methionine synthesis in Escherichia coli by analogues of cobalamin

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Abstract
Under certain conditions cobalamin is required for the snythesis of methionine by ultrasonic extracts of strains of Escherichia coli. The action of cobalamin is inhibited by the methylamide, ethylamide and anilide of the monocarboxylic acids of cobalamin and by factor B. The anilide analogue inhibits compeitively both the action of cobalamin and of 5,6-dimethyl-benzimidazole B12-coenzyme, but is less active against the latter. When an extract of heated oranisms is used as source of folic acid coenzyme with enzymic extracts of a strain not requiring cobalamina for growth, cobalamin is not required for methionine synthesis and the analogues are not inhibitory. Extracts of organisms grown in the presence of cobalamin do not require added cobalamin for methionine synthesis and the anilide analogue again does not inhibit. The anilide analogue inhibits the growth of strains requiring cobalamin or methionine for growth when cobalamin is the growth factor, but not when methionine is supplied. It does not inhibit the growth of strains which do not require cobalamin for growth.