Biosynthesis of trigonelline.

Trigonelline, N-methyl nicotinic acid, was first noted in the seeds of Trigonella joenum-graecum (the fenugreek) (1) and has since been found in the seeds and tubers of many species (2,3) as well as in leaves of one species of pea (4). Although one may assume that trigonelline arises metabolically from nicotinic acid, definitive evidence has been lacking. In the course of several attempts to demonstrate formation of nicotinic acid from tryptophan by higher plants, administration of CY4-labeled tryptophan (5, 6) or 3-hydroxyanthranillic acid-7-V (7) did not result in the appearance of either labeled nicotinic acid or trigonelline. In the studies to be reported below, it has been demonstrated that trigonelline synthesis in the green pea, Pisum sativum, proceeds in a manner analogous to the formation of iv-methyl nicotinamide in rat liver (8)) i.e. methylation is accomplished by reaction between nicotinic acid and S-adenosyl methionine.