Catabolism of caffeine and related purine alkaloids in leaves of Coffea arabica L
1996
Ashihara, H. | Monteiro, A.M. | Moritz, T. | Gillies, F.M. | Crozier, A.
In a study of purine alkaloid catabolism pathways in coffee, 14C-labelled theobromine, caffeine, theophylline and xanthine were incubated with leaves of Coffea arabica. Incorporation of label into 14CO2 was determined and methanol-soluble metabolites were analysed by high-performance liquid chromatography-radiocounting. The data obtained demonstrate catabolism of caffeine leads to theophylline leads to 3-methylxanthine leads to xanthine. Xanthine is degraded further by the conventional purine catabolism pathway to CO2 and NH3 via uric acid, allantoin and allantoic acid. The conversion of caffeine to theophylline is the rate-limiting step in purine alkaloid catabolism and provides a ready explanation for the high concentration of endogenous caffeine found in C. arabica leaves. Although theobromine is converted primarily to caffeine, a small portion of the theobromine pool appears to be degraded to xanthine by a caffeine-independent pathway. In addition to being broken down to CO2, via the purine catabolism pathway, xanthine is metabolised to 7-methylxanthine. Metabolism of [2-14C]xanthine by C. arabica leaves in the presence of 5 mM allopurinol results in very large increases in incorporation of radioactivity into 7-methylxanthine as degradation of the substrate via the purine catabolism pathway is blocked. The identity of 7-methylxanthine in these studies was confirmed by gas chromatography-mass spectrometry analysis.
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