Involved in the biosynthesis of caffeine in cv. Puer. Involved in the biosynthesis of theacrine in cv. Kucha, a caffeine-like xanthine alkaloid with diverse beneficial biological activities including anti-depressive, sedative, and hypnotic activities, improving learning and memory, increasing exercise activity, and preventing nonalcoholic fatty liver disease. Catalyzes the conversion of 7-methylxanthine (7mX) to theobromine but not able to convert paraxanthine to caffeine