The biogenesis of caffeine is probably similar in all plants, but with differences in the rates of various steps. It has its origin in the cell purine pool. Precursors include 7-methylxanthosine, 7-methylxanthine, and theobromine. Synthesis of caffeine from adenine occurs readily in young tea leaf. 7-Methylguanilic acid and 7-methylguanasine are also on the biosynthetic path. A 7-methyl-AT-nucleoside hydrolase mediates the removal of ribose from 7-methylxan-thosine. S-adenosylmethionine is the methyl donor for the methylation of the xanthines in reactions catalyzed by N-methyltransferase (12,13). A possible reaction path is shown in Figure 3. Caffeine biosyntheses in the coffee plant (12-14) and in the tea plant (14-16) have been studied in detail.
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