A new caffeine biosynthetic pathway in tea leaves: utilisation of adenosine released from the S‐adenosyl‐L‐methionine cycle

Abstract

The four-step caffeine biosynthetic pathway includes three methylation steps that utilise S-adenosyl-L-methionine (SAM) as the methyl donor. In the process SAM is converted to S-adenosyl-L-homocysteine (SAH) which in turn is hydrolysed to L-homocysteine and adenosine. Significant amounts of radioactivity from [methyl-14 C]methionine and [methyl-14 C]SAM were incorporated into theobromine and caffeine in young tea leaf segments, and very high SAH hydrolase activity was found in cell-free extracts from young tea leaves. Substantial amounts of radioactivity from [adenosyl-14 C]SAH were also recovered as theobromine and caffeine in tea leaf segments, indicating that adenosine derived from SAH is utilised for the synthesis of the purine ring of caffeine. From the profiles of activity of related enzymes in tea leaf extracts, it is proposed that the major route from SAM to caffeine is a SAMC CSAHC CadenosineC CadenineC CAMPC CIMPC CXMPC CxanthosineC C7-methylxanthosineC C7-methylxanthineC CtheobromineC Ccaffeine pathway. In addition, direct adenosine kinase-catalysed formation of AMP from adenosine may participate as an alternative minor route. The activity of two of the three N-methyltransferase activities involved in caffeine biosynthesis and part of the activities of SAH hydrolase, adenosine nucleosidase, adenine phosphoribosyltransferase and adenosine kinase were located in tea chloroplasts. In contrast, no detectable activity of SAM synthetase was associated with the purified chloroplast fraction. This is a first demonstration that the purine skeleton of caffeine is synthesised from adenosine released from the SAM cycle. ß

Microbial community gene expression within colonies of the diazotroph, Trichodesmium, from the Southwest Pacific Ocean

“…Trichodesmium transcripts included those implicated in sulfur metabolism, including methionine (Koshiishi et al, 2001). Trichodesmium has extensively methylated adenine in its genomic DNA (15 mol%) (Zehr et al, 1991).…”

Purine and Pyrimidine Nucleotide Synthesis and Metabolism

“…None of the predicted amino acid sequences for the Arabidopsis APTs appear to contain transit signaling peptides although APTs have been localized to plastids and mitochondria in other plants (Hirose and Ashihara, 1982;Le Floc'h and Lafleuriel, 1983;Wasternack et al, 1985;Koshiishi et al, 2001). To investigate the subcellular localization of APT1, 2 and 3, peptide antibodies specific for each isoform were prepared and used to probe immunoblots of subcellular fractions of Arabidopsis leaves.…”

Immunohistochemical localization of caffeine in young Camellia sinensis (L.) O. Kuntze (tea) leaves

“…Caffeine synthase has been located within the chloroplasts of young leaves (Kato et al 1998;Koshiishi et al 2001) specifically thought to be in the stroma (Kato et al 1999). Alkaloids in general do not show the same patterns of localization.…”