Caffeine synthase is a methyltransferase enzyme involved in the caffeine biosynthesis pathway. It is expressed in tea species, coffee species, and cocoa species. The enzyme catalyses three related reactions:
The first is the final methylation step in the biosynthesis of caffeine from xanthosine via theobromine. The methyl group comes from the cofactor, S-adenosyl methionine (SAM), which becomes S-adenosyl-L-homocysteine (SAH).
The second is the reaction which produces theobromine from 7-methylxanthine, a reaction also catalysed by theobromine synthase:
Finally, the enyme also converts paraxanthine to caffeine:
Caffeine synthase is expressed in the Camellia species irrawadiensis, ptilophylla, and sinensis; the Coffea species arabica, and canephora; and in Theobroma cacao.
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