Ureide Synthesis in a Cell-Free System from Cowpea (Vigna unguiculata [L.] Walp.) Nodules 1: STUDIES WITH O2, pH, AND PURINE METABOLITES

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RESUMO

The effect of O2 and pH on the in vitro synthesis of 14C-labeled ureides from [8-14C]hypoxanthine in a cell-free system from cowpea nodules was investigated. Under conditions which suppressed uricase (EC 1.7.3.3) activity, namely low O2 concentrations and low pH, ureide synthesis was inhibited and the 14C label incorporated into uric acid was increased. Conversely, conditions which increased uricase activity, namely high O2 concentrations and high pH, also stimulated ureide synthesis, and the 14C label was incorporated principally into allantoin. The overall response of the system to O2 concentration and pH indicated that the per cent distribution of total 14C 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 [8-14C]hypoxanthine was also inhibited.

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