35 チャ、コーヒー植物のプリンアルカロイドの生合成と植物生理的意義

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Purine alkaloids (caffeine and other methylxanthines) are important nitrogen compounds in non-alcoholic beverages prepared from caffeine-containing plants, i.e., cocoa, coffee, cola, guarana, mate, tea and so on. We have demonstrated that caffeine is synthesized in tea and coffee plants through the steps: purine nucleotides in nucleotide pool (AMP and/or GMP→IMP→XMP)→xanthosine→7-methylxanthosine→7-methylxanthine→theobromine→caffeine. Evidence was obtained that purine biosyntheses de novo and by salvage pathways are separately compartmentalized in tea shoot tips. Administration of [8-^<14>C]hypoxanthine or [8-^<14>C]guanine showed a preferential incorporation of ^<14>C into the GMP of RNA, while there was more incorporation of [1-^<14>C]glycine or [^<14>C]methylamine into AMP of RNA than GMP of RNA. Further, after administration of a 'pulse' of [8-^<14>C]adenine, almost all of the [8-^<14>C]adenine supplied disappeared by 30h, and ^<14>C-labeled caffeine and purine nucleotide (AMP and GMP) synthesis increased throughout the experimental period, whereas the ^<14>C of xanthosine, 7-methylxanthosine, 7-methylxanthine and theobromine increased during the first 10h incubation period, followed by a steady decrease. Extracts prepared from tea leaves or fruits and callus cultures of coffee with Polyclar AT contained three methyltransferase activities catalysing the transfer of methyl groups from S-adenosylmethionine to xanthosine, producing 7-methylxanthosine, to 7-methylxanthine, producing theobromine, and to theobromine, producing caffeine, respectively. Similar extracts from coffee fruits or callus cultures exhibited 7-methyl-N^9-nucleoside hydrolase activity, which is responsible for the hydrolysis of 7-methylxanthosine to 7-methylxanthine and D-ribose. The metabolism (biodegradation), physiological significance and ecological function of purine alkaloids in tea and coffee plants are also discussed.
天然有機化合物討論会の論文
1986-09-09

35 チャ、コーヒー植物のプリンアルカロイドの生合成と植物生理的意義

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