Folic acid and the synthesis of methionine by extracts of Escherichia coli

Abstract

Tetra-hydropteroyltriglutamate, its N5- and N10-formyl derivatives and an extract of heated Escherichia coli are each able to serve as source of folic acid cofactor for methionine synthesis by ultrasonic extracts of E. coli PA 15 in the absence of added cobalamin. Tetrahydropteroyl-glutamate requires added cobaiamin for activity. Pteroylglutamate, pteroyltriglutamate, and N10-formylpteroyltriglutamate are devoid of cofactor activity. The Km values for the synthetic compounds are tetrahydropteroylglutamate (with 77 uumoles of cobalamin), 180 [mu][image]; tetrahydropteroyltriglutamate and its NlO-formyl derivative, both 8 [mu]M; N5-formyltetrahydropteroyltriglutamate, 1.6 [mu][image]. The folic acid con-centration of a reaction mixture giving half-maximal methionine synthesis with extract of heated E. coli is 0.4-3 [mu][image], depending upon the assay organism employed.