FORMATION OF METHIONINE FROM MONOGLUTAMATE FORM OF METHYLTETRAHYDROFOLATE BY HIGHER PLANTS

A dialyzed extract of green string beans has been found to catalyze the transmethylation of homocysteine with CH3-H4PteGlu31 1 Abbreviations for members of the folic acid group: PteGlu, pteroylmonoglutamate; PteGlu3, pteroyl-γ-glutamyl-γ-glutamyl-glutamate; folate, all members of the group. CH3-H4-, the N5-methyl-tetrahydroderivative. and, at a slower rate, with CH3-H4PteGlu. The transmethylation of these substrates neither required nor was increased by the addition of S-adenosylmethionine and a reducing system to the incubation mixtures and therefore could not have been due to a B12-dependent methyltransferase. Transmethylase activities for both CH3-H4-folates were eluted from Sephadex G-100 in the same fractions. The results are interpreted as indicating that green string beans possess a methyltransferase similar to the B12-independent enzyme of microorganisms but capable of utilizing the monoglutamate as well as polyglutamate forms of CH3-H4 folate. Preliminary studies suggest that this type of enzyme may be widely distributed in higher plants. © 1969.