The Biosynthesis of 4-Methylsulfinyl-3-butenylglucosinolate (Glucoraphenin) in M atthiola Species Evidence for Homomethionine and 2-Amino-6-methylthiocaproic Acid as Intermediates

[35S] L-Methionine and [methyl-14C] L-methionine were fed to shoots of M atth iola annua and M atthiola sinuata. The label from both precursors was incorporated to a high degree into 4-methylsulfinyl-3-butenylglucosinolate, the main mustard oil glucoside of M atth iola species. Two homologues of methionine, homomethionine and 2-amino-6-methylthiocaproic acid, were also labelled in these experiments. 2-Amino-6-methylthiocaproic acid, deriving from methionine via homomethionine by two successive Cj-chain elongation steps, was higher plants.