Cobalamin and the enzymic formation of a factor concerned in the synthesis of methionine by Escherichia coli

Abstract

A heat-labile, non-diffusible material was partly purified from the products of the incubation of ultrasonic extracts of E. coli strain PA 15 with cobalamin, glucose, adenosine triphosphate, Mg2+ ions, diphosphopyridine nucleotide and phosphate buffer. This factor is essential for the synthesis of methionine by extracts of acetone-dried organisms of the same strain when tetrahydropteroylglutamate acts as source of the necessary folic acid cofactor for the C1 transfer reaction. The factor has similar properties to material with the same biological activity previously isolated from the same organism grown in the presence of added cobalamin. Monosubstituted cobalamin-amide analogues inhibit the formation of the factor by the ultrasonic extracts but have no effect upon its function in methionine synthesis. Factor B partially inhibits both the formation and the function of the factor. A method for assaying the factor formed by ultrasonic extracts is described. It makes use of the ability of analogues of cobalamin to inhibit formation of the factor. 5:6-Dimethylbenzimidazolylcobamide-coenzyme has no activity as the factor but replaces cobalamin for its formation.