IUBMB Enzyme Nomenclature


Accepted name: 7-methylxanthosine synthase

Reaction: S-adenosyl-L-methionine + xanthosine = S-adenosyl-L-homocysteine + 7-methylxanthosine

For diagram of reaction click here

Other name(s): xanthosine methyltransferase; XMT; xanthosine:S-adenosyl-L-methionine methyltransferase; CtCS1; CmXRS1; CaXMT1; CmXRS1; S-adenosyl-L-methionine:xanthosine 7-N-methyltransferase

Systematic name: S-adenosyl-L-methionine:xanthosine N7-methyltransferase

Comments: The enzyme is specific for xanthosine, as XMP and xanthine cannot act as substrates [2,4]. The enzyme does not have N1- or N3- methylation activity [2]. This is the first methylation step in the production of caffeine.

Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, PDB, CAS registry number:


1. Negishi, O., Ozawa, T. and Imagawa, H. The role of xanthosine in the biosynthesis of caffeine in coffee plants. Agric. Biol. Chem. 49 (1985) 2221-2222.

2. Mizuno, K., Kato, M., Irino, F., Yoneyama, N., Fujimura, T. and Ashihara, H. The first committed step reaction of caffeine biosynthesis: 7-methylxanthosine synthase is closely homologous to caffeine synthases in coffee (Coffea arabica L.). FEBS Lett. 547 (2003) 56-60. [PMID: 12860386]

3. Uefuji, H., Ogita, S., Yamaguchi, Y., Koizumi, N. and Sano, H. Molecular cloning and functional characterization of three distinct N-methyltransferases involved in the caffeine biosynthetic pathway in coffee plants. Plant Physiol. 132 (2003) 372-380. [PMID: 12746542]

4. Yoneyama, N., Morimoto, H., Ye, C.X., Ashihara, H., Mizuno, K. and Kato, M. Substrate specificity of N-methyltransferase involved in purine alkaloids synthesis is dependent upon one amino acid residue of the enzyme. Mol. Genet. Genomics 275 (2006) 125-135. [PMID: 16333668]

[EC created 2007]

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