This family of plant methyltransferases contains enzymes that act on a variety of substrates including salicylic acid, jasmonic acid and 7-Methylxanthine. Caffeine is synthesised through sequential three-step methylation of xanthine derivatives at positions 7-N, 3-N, and 1-N. The protein 7-methylxanthine methyltransferase (designated as CaMXMT) catalyses the second step to produce theobromine [1].

1: 7-Methylxanthine methyltransferase of coffee plants. Gene isolation and enzymatic properties. Ogawa M, Herai Y, Koizumi N, Kusano T, Sano H; J Biol Chem 2001;276:8213-8218. PMID:11108716

2: Caffeine synthase gene from tea leaves. Kato M, Mizuno K, Crozier A, Fujimura T, Ashihara H; Nature 2000;406:956-957. PMID:10984041

3: Jasmonic acid carboxyl methyltransferase: a key enzyme for jasmonate-regulated plant responses. Seo HS, Song JT, Cheong JJ, Lee YH, Lee YW, Hwang I, Lee JS, Choi YD; Proc Natl Acad Sci U S A 2001;98:4788-4793. PMID:11287667

4: Developmental regulation of methyl benzoate biosynthesis and emission in snapdragon flowers. Dudareva N, Murfitt LM, Mann CJ, Gorenstein N, Kolosova N, Kish CM, Bonham C, Wood K; Plant Cell 2000;12:949-961. PMID:10852939