“…Additional evidence that theobromine is an immediate precursor of caffeine was provided by studies using tea leaves: (a) radiolabeled adenine (Ashihara and Kubota, 1986;Fujimori and Ashihara, 1990;Fujimori et al, 1991), guanine, and hypoxanthine Takahashi, 1976a, 1976b;Ashihara and Kubota, 1987) were incorporated into theobromine and caffeine to a greater extent than into theophylline by intact leaves; (b) during leaf development, theobromine content decreased as the concentration of caffeine increased (Ashihara and Kubota, 1986); and (c) cell-free extracts of tea leaves converted 7-methylxanthosine and 7-methylxanthine to both theobromine and caffeine (Suzuki and Takahashi, 1975a;Negishi et al, 1985aNegishi et al, , 1985bFujimori et al, 1991).…”