The Enzyme Database

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Accepted name: 7-methylxanthosine synthase
Reaction: S-adenosyl-L-methionine + xanthosine = S-adenosyl-L-homocysteine + 7-methylxanthosine
For diagram of caffeine biosynthesis, click here
Other name(s): xanthosine methyltransferase; XMT; xanthosine:S-adenosyl-L-methionine methyltransferase; CtCS1; CmXRS1; CaXMT1; 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
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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