Abstract
Summary The activity of phosphoribosylpyrophosphate synthetase (PRPP synthetase, EC 2.7.6.1), partially purified from spinach leaves, was assayed in the presence of a variety of biological compounds to test for their possible regulatory effects. 1. The activity of spinach PRPP synthetase is influenced by the ≪adenylate energy charge≫, although the response of the enzyme is less than that obtained in typical ATP-utilizing enzymes controlled by the -energy charge-. 2. The enzyme activity is activated by Mg2+, and is probably inhibited by free ATP. 3. A variety of nucleoside monophosphate (NMP) and nucleoside diphosphate (NDP) inhibits the enzyme activity. Nucleoside triphosphates (NTP) are much less effective than NMP and NDP. The inhibition by NMP and NDP is not relieved by inorganic phosphate (Pi). 4. Little or no inhibition of the activity by NAD2+, NADP2+, histidine, and tryptophan was found. 5. The activity of the enzyme is not influenced by certain plant growth regulators, including indoleacetic acid, 2,4-dichlorophenoxyacetic acid, giberellic acid, kinetin, and 3',5'-cyclic AMP. 6. The observed properties of PRPP synthetase is discussed in relation to the regulation of the PRPP synthesis in plant tissue.
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