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Articles

Ureide Synthesis in a Cell-Free System from Cowpea (Vigna unguiculata [L.] Walp.) Nodules ¹

STUDIES WITH O₂, pH, AND PURINE METABOLITES

Craig A. Atkins and John S. Pate

Department of Environmental Biology, Research School of Biological Sciences, Australian National University, P.O. Box 475, Canberra City, A.C.T. 2601, Australia, Department of Botany, University of Western Australia, Nedlands, Western Australia 6009

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.