Purine metabolism and the biosynthesis of caffeine in maté leaves

Purine metabolism and the biosynthesis of purine alkaloids in leaves of maté plants were investigated by administering [8-14C]adenine,[8-14C]guanosine and [8-14C]hypoxanthine to maté plants of different ages. Each precursor was incorporated into theobromine and caffeine in young leaves. No biosynthesis of these purine alkaloids took place in mature dark-green leaves. Pulse-chase experiments and the inhibitory effects of coformycin suggest that the biosynthesis of caffeine from adenine nucleotides is initiated by the reaction catalysed by AMP deaminase. The conventional pathway for the degradation of purines via allantoin and allantoic acid appeared to be operative in both young and mature leaves. No significant degradation of caffeine was detected in the tracer experiments. The levels of adenine nucleotides in young maté leaves were about five times higher than those of guanine nucleotides. Other possible pathways of purine metabolism in maté leaves are discussed.