Abstract
In a study of purine alkaloid catabolism pathways in coffee,14C-labelled theobromine, caffeine, theophylline and xanthine were incubated with leaves ofCoffea arabica. Incorporation of label into14CO2 was determined and methanol-soluble metabolites were analysed by high-performance liquid chromatography-radiocounting. The data obtained demonstrate catabolism of caffeine → theophylline → 3-methylxanthine → 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 inC. 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 byC. 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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Abbreviations
- HPLC-RC:
-
high-performance liquid chromatography-radiocounting
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This work was supported by the British Council which provided H.A. with Japan-UK travel grants. F.M.G. was supported by a Biotechnology and Biological Sciences Research Council grant to A.C.
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Ashihara, H., Monteiro, A.M., Moritz, T. et al. Catabolism of caffeine and related purine alkaloids in leaves ofCoffea arabica L.. Planta 198, 334–339 (1996). https://doi.org/10.1007/BF00620048
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DOI: https://doi.org/10.1007/BF00620048