Metabolism of methylamine in the tea plant (Thea sinensis L.).

1. The metabolism of methylamine in excised shoot tips of tea was studied with micromolar amounts of [(14)C]methylamine. Of the [(14)C]methylamine supplied 57% was utilized by tea shoots during the 10h experimental period. 2. The main products of [(14)C]methylamine metabolism in tea shoots were serine, gamma-glutamylmethylamide, theobromine, caffeine and CO(2). There was also incorporation of the label into glutamate, aspartate, RNA purine nucleotides and S-adenosylmethionine. 3. The formation of methylamine from gamma-glutamylmethylamide was confirmed by feeding tea shoots with gamma-glutamyl[(14)C]methylamide. The products of gamma-glutamyl[(14)C]methylamide metabolism in tea plants were serine, theobromine, caffeine, glutamate and aspartate. 4. The results indicate that the oxidation of methylamine to formaldehyde is the first step of methylamine utilization. Labelled formaldehyde released by the metabolism of methylamine leads to the incorporation of the label into metabolites on the C(1) pathways of this compound. It is also suggested that formaldehyde is further oxidized via formate to CO(2). 5. The role of gamma-glutamylmethylamide in methylamine metabolism in tea plants is discussed. 6. Results support the view that theobromine is the immediate precursor of caffeine.