Biosynthesis of Caffeine in Flower Buds of Camellia sinensis

Abstract

The biosynthesis of purine alkaloids in flower buds of tea plants was investigated. More than 25% of total radioactivity of [8-14C]adenine taken up by stamens isolated from tea flower buds was found to have been incorporated into purine alkaloids, namely, theobromine and caffeine, 24 h after administration of the labelled compound. Pulse-chase experiments indicated that [8-14C]adenine taken up by the stamens was converted to adenine nucleotides and subsequently incorporated into theobromine and caffeine. Since 5 μM coformycin, an inhibitor of AMP deaminase, inhibited the incorporation of radioactivity into the purine alkaloids, synthesis of caffeine from adenine nucleotides seems to be initiated by the reaction of AMP deaminase. Although most of the radioactivity from [8-14C]inosine was recovered as CO2 and ureides, considerable amounts of radioactivity were recovered as purine alkaloids. The incorporation of radioactivity from [8-14C]inosine into the purine alkaloids was not affected by coformycin. The five enzymes involved in synthesis of 5-phosphoribosyl-1-pyrophosphate from glucose were present in the stamens and petals of tea flower buds. From present and previous results, the pathway for the biosynthesis of caffeine from adenine nucleotides in flower buds of tea is discussed.