The Origin of the O- And N-Methyl Groups of the Alkaloid Ricinine

There is a rapidly increasing body of evidence in the literature indicating that all biological methylation processes have a common pattern.It has recently been shown that the methyl groups of the alkaloids hordenine (1, 2) and nicotine (3) have the same origin as the so called labile methyl groups in animal metabolism.Kirkwood and Marion (2) have reported that the methyl groups of both hordenine and choline synthesized by the barley plant are derived from formate carbon.There is, however, no transfer of labeled choline methyl to hordenine.Brown and Byerrum (3) have reported that both the methyl carbon of methionine and formate carbon serve as precursors of the N-methyl group of the alkaloid nicotine.These authors postulate that formate serves as a precursor of the labile methyl groups in the plant which undergo transmethylation to nicotine.Matchett, Marion, and Kirkwood' have investigated the r61e of methionine in the origin of the methyl groups of hordenine.The administration of C*4-methyl-labeled L-methionine to barley plants results in a high activity in the methyl groups of this alkaloid and of choline.Thus in barley there is a rapid transfer of methyl groups from methionine to hordenine and choline, but no transfer of the methyl group from choline to methionine such as has been shown to occur in animals (4).This work, along with that of Brown and Byerrum, points to methionine having a key position in the synthesis and transfer of the labile methyl group in plants.Enzyme CHa