Cobalamin and the synthesis of methionine by ultrasonic extracts of Escherichia coli

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Abstract
Ultrasonic extacts of Escherichia coli strain 121/176 (a cobalamin or methionine auxotroph) and of strain PA 15 (a serine or g glycine auxotroph) synthesize methionine from homocysteine and serine under certain conditions in the presence of glucose, adenosine triphosphate, magnesium ions, diphosphopyridine nucleotide (DPN) and a source of natural folic acid (extract of heated organism). With strain 121/176 the further provision of cobalamin is necessary if the organism has been grown originally on a medium devoid of this vitamin. Natural folic acid can be replaced by tetrahydropteroylglutamate. With strain PA 15 cobalamin is not required if the natural source of folic acid coenzyme is provided. Tetrahydropteroylglutamate can, however, only be used if cobalamin is present. The formaldehyde derivative of tetrahydropteroylglutamate can serve with both strains both as source of folic acid coenzyme and of C1 units provided again that cobalamin is present. Growth of either strain in the presence of cobalamin enhances the ability of ultrasonic extracts of the organisms to methylate homocysteine. Reduced -DPN abolishes the requirement for both glucose and DPN.