Xanthine degradation and related enzyme activities in leaves and fruits of two coffea species differing in caffeine catabolism.

The degradation of xanthine was studied in young and aged leaves and in immature and mature fruits of Coffea arabica and Coffea dewevrei, which differ with respect to caffeine catabolism. Radioisotope feeding experiments showed that leaves degraded xanthine more readily than fruits but that mature fruits and aged leaves were less efficient than younger tissues. In all cases, a significant part of the recovered radioactivity was in the ureides. Xanthine dehydrogenase was characterized as the enzyme responsible for xanthine degradation, and its activity and that of uricase were consistent with the results obtained in the radioisotope feeding experiments. Activities of allantoinase and allantoate amidohydrolase could not be detected. Considerable levels of endogenous allantoin and allantoic acid were found in fruits and leaves. Therefore, ureide accumulation might be a consequence of low enzyme activity. There was no positive correlation between urease activity and the data from the radioisotope feeding experiments.