Ureide Synthesis in a Cell-Free System from Cowpea (Vigna unguiculata [L.] Walp.) Nodules

The effect of O(2) and pH on the in vitro synthesis of (14)C-labeled ureides from [8-(14)C]hypoxanthine in a cell-free system from cowpea nodules was investigated. Under conditions which suppressed uricase (EC 1.7.3.3) activity, namely low O(2) concentrations and low pH, ureide synthesis was inhibited and the (14)C label incorporated into uric acid was increased. Conversely, conditions which increased uricase activity, namely high O(2) concentrations and high pH, also stimulated ureide synthesis, and the (14)C label was incorporated principally into allantoin. The overall response of the system to O(2) concentration and pH indicated that the per cent distribution of total (14)C label incorporated into uric acid was inversely related to that into allantoin. In the present study there was evidence that uricase (EC 1.7.3.3) controlled the in vitro rate of ureide synthesis in the cell-free system. Adenine and guanine inhibited xanthine dehydrogenase (EC 1.2.1.37) and as a consequence ureide synthesis from [8-(14)C]hypoxanthine was also inhibited.