Reaction: S-adenosyl-L-methionine + 7-methylxanthine = S-adenosyl-L-homocysteine + 3,7-dimethylxanthine
For diagram of reaction click here
Glossary: theobromine = 3,7-dimethylxanthine
paraxanthine = 1,7-dimethylxanthine
Other name(s): monomethylxanthine methyltransferase; MXMT; CTS1; CTS2; S-adenosyl-L-methionine:7-methylxanthine 3-N-methyltransferase
Systematic name: S-adenosyl-L-methionine:7-methylxanthine N3-methyltransferase
Comments: This is the third enzyme in the caffeine-biosynthesis pathway. This enzyme can also catalyse the conversion of paraxanthine into caffeine, although the paraxanthine pathway is considered to be a minor pathway for caffeine biosynthesis [2,3].
Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, CAS registry number:
References:
1. Ogawa, M., Herai, Y., Koizumi, N., Kusano, T. and Sano, H. 7-Methylxanthine methyltransferase of coffee plants. Gene isolation and enzymatic properties. J. Biol. Chem. 276 (2001) 8213-8218. [PMID: 11108716]
2. 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]
3. 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]