Theophylline metabolism in higher plants.

Metabolism of [8-(14)C]theophylline was investigated in leaf segments from Camellia sinensis (tea), Camellia irrawadiensis, Ilex paraguariensis (maté) and Avena sativa, root segments of Vigna mungo seedlings and cell suspension cultures of Catharanthus roseus. There was extensive uptake and metabolism of [8-(14)C]theophylline by leaves of tea and Camellia irrawadiensis and, to a lesser extent, maté. These purine alkaloid-containing species converted [8-(14)C]theophylline into 3-methylxanthine, xanthine, the ureides allantoin and allantoic acid, and CO2. With the other test systems, which were from species that do not produce purine alkaloids, there were low levels of [8-(14)C]theophylline uptake which were accompanied by incorporation of relatively small amounts of label into 3-methylxanthine, xanthine and CO2. None of the higher plants converted [8-(14)C]theophylline to either 1-methyluric acid or 1,3-dimethyluric acid, which are the main catabolites of theophylline in mammals. The data indicate that the main route of theophylline degradation in higher plants involves a theophylline --> 3-methylxanthine --> xanthine --> uric acid --> allantoin --> allantoic acid --> --> CO2 + NH3 pathway. In tea and mate, large amounts of [8-(14)C]theophylline were also converted to theobromine and caffeine via a theophylline --> 3-methylxanthine --> theobromine --> caffeine salvage pathway. The diversity of theophylline metabolism in higher plants and mammals is discussed.