CAFFEINE BIOSYNTHESIS AND PURINE METABOLISM IN LEAVES OF MASCAROCOFFEA SPECIES
Caffeine, a purine alkaloid, was not detected in leaves of two Mascarocoffea species, Coffea millotii and Coffea perrier. Trigonelline, a pyridine alkaloid, occurred in these species, but the levels (3−4 μmol/g fresh weight) were much lower than that of Robusta coffee (Coffea canephora) (36 μmol/g fresh weight). Feeding experiments with [8-14C]adenine indicated that purine alkaloid biosynthesis was terminated at 7-methylxanthine formation and as a consequence theobromine and caffeine were not produced in Coffea millotii and Coffea perrier. The adenine salvage activity was lower but its degradation activity was higher in leaves of these Mascarocoffea species than those in Coffea canephora. The metabolic fate of the purine nucleosides, [8-14C]inosine, [8-14C]guanosine and [8-14C]xanthosine was investigated in leaves of Coffea millotii. The biosynthesis of 7-methylxanthine, but not theobromine or caffeine, from these precursors was detected. Large amounts of these purine nucleosides were catabolized via allantoin. Limited amounts of [8-14C]inosine and [8-14C]guanosine were salvaged and utilized for RNA synthesis, however, no [8-14C]xanthosine salvage was observed. Little or no 14C-metabolites were observed when [8-14C]theobromine and [8-14C]caffeine were applied to leaf disks of Coffea millotii. From the results obtained in this study, possible metabolic pathways of purines in Mascarocoffea species are discussed.
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