Methyl derivatives of folic acid as intermediates in the methylation of homocysteine by Escherichia coli

Two enzymic mechanisms for the methylation of homocysteine by extracts of Escherichia coli

“…The functions of these cofactors have been investigated and are described and discussed by Guest et al (1964a) and Guest, Friedman, Foster, Tejerina & Woods (1964b).…”

A simple method for the preparation of 5-methyltetrahydropteroylglutamic acid

“…The absorption at 289m,u differs from that of 5,10 -methylidynetetrahydropteroylglutamic acid, which has a peak at 350m,u, and from that of 5,10-methylenetetrahydropteroylglutamic acid, which absorbs maximally at 295m,u. There does not appear to be a clear difference in absorption at acid pH between the methyl and 5,10-methylene compounds, peak absorption being at 268 and 292m,u (Guest, Foster & Woods, 1964;Osborne, Talbert & Huennekens, 1960). Residual borate can be removed on a DEAE-cellulose column (Keresztesy & Donaldson, 1961).…”

Folic acid and the methylation of homocysteine by Bacillus subtilis

“…E. coli strains 121/176 and 113/3 are cobalamin or methionine auxotrophs (Davis & Mingioli, 1950) and lack 5-CH3-H4PteGlu3-homocysteine transmethylase (Foster et al, 1964b). E. coli strain 3/62, which lacks 5,10-methylenetetrahydrofolate reductase (Guest et al, 1964a), responds to methionine but not to cobalamin or homocysteine.…”

“…Background colour was not significant provided the depth of agar was less than 3 mm above the glass plate. Chemicals (±)-5-[14C]Methyltetrahydrofolates were prepared by reduction of (±)-5,10-[14C]methylenetetrahydrofolates with NaBH4 and purified by column chromatography as described by Guest et al (1964a). Solutions in potassium phosphate buffer, pH7.5 (50mM), containing 2-mercaptoethanol (7mM), were standardized spectrophotometrically (by using E= 28000 litre molV-cm-1 at 290nm) and the specific radioactivity was determined by scintillation counting of diluted samples.…”

“…The methyl group of methionine has been shown to arise in various organisms by the enzymic reduction of 5,10-methylenetetrahydrofolate, the C1 unit being derived from C-3 of serine via serine transhydroxymethylase (L-serine-tetrahydrofolate 5,10-hydroxymethyltransferase, EC 2.1.2.1) (Larrabee & Buchanan, 1961;Cauthen et al, 1966Cauthen et al, , 1967Sakami & Ukstins, 1961;Kutzbach & Stokstad, 1966. In Escherichia coli, the enzymic generation of methyl groups can occur with either H4PteGlu1t or H4PteGlu3 as Cl-unit carrier (Guest et al, 1964a). E. coli has alternative enzymic mechanisms for the methylation of homocysteine by 5-methyltetrahydrofolate (Woods et al, 1965).…”