Further investigation of the biosynthesis of caffeine in tea plants (Camellia sinensis L.). Methylation of transfer ribonucleic acid by tea leaf extracts

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Abstract
The tRNA methyltransferase activity in vitro of leaves, cotyledons and roots of 85 day old tea seedlings was studied. The activity of extracts prepared from tea leaves with Polyclar AT (insoluble polyvinylpyrrolidine) had optimum pH 7.7 and was greatly influenced by thiol compounds, but only slightly by metal ions and ammonium acetate. The activities of extracts, expressed per milligram of protein, were as follows: roots > leaves > cotyledons. The only methylated base isolated after incubation with these preparations was 1-methyladenine. The results did not support the view of involvement of methylation of nucleic acids in caffeine biosynthesis in tea plants. It is suggested that theophylline is synthesized from the specific methylated precursor in nucleic acids, i.e. 1-methyladenylic acid, via 1-methylxanthine.