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Title

The first committed step reaction of caffeine biosynthesis: 7-methylxanthosine synthase is closely homologous to caffeine synthases in coffee (Coffea arabica L.)<sup>1</sup><FN ID="FN1"><NO>1</NO>The nucleotide sequence data reported here will appear in the EMBL, GenBank and DDBJ Nucleotide Sequence Databases under the accession number AB034699 (CmXRS1).</FN>

Authors

Mizuno, Kouichi; Kato, Misako; Irino, Fumi; Yoneyama, Naho; Fujimura, Tatsuhito; Ashihara, Hiroshi

Abstract

In coffee and tea plants, caffeine is synthesized from xanthosine via a pathway that has three methylation steps. We identified and characterized the gene encoding the enzyme for the first methylation step of caffeine biosynthesis. The full-length cDNA of coffee tentative caffeine synthase 1, CtCS1, previously isolated by the rapid amplification of cDNA ends was translated with an Escherichia coli expression system and the resultant recombinant protein was purified using Ni-NTA column. The protein renamed CmXRS1 has 7-methylxanthine synthase (xanthosine:S-adenosyl-L-methionine methyltransferase) activity. CmXRS1 was specific for xanthosine and xanthosine 5′-monophosphate (XMP) could not be used as a substrate. The Km value for xanthosine was 73.7 μM. CmXRS1 is homologous to coffee genes encoding enzymes for the second and third methylation steps of caffeine biosynthesis.

Subjects

CAFFEINE; METHYLATION; BIOSYNTHESIS

Publication

FEBS Letters, 2003, Vol 547, Issue 1-3, p56

ISSN

0014-5793

Publication type

Academic Journal

DOI

10.1016/S0014-5793(03)00670-7