Nucleoside diphosphokinase of pea seeds

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Abstract
Nucleoside diphosphokinase, which catalyzes the reaction adenosine uridine adenosine uridine triphosphate + diphosphate diphosphate triphosphate was found in pea-seed extracts. Preparations free from interfering enzyme reactions were readily obtained. The apparent equilibrium constant ([adenosine diphosphate] [uridine triphosphate]/[adenosine triphosphate] [uridine diphosphate]) was determined. Increase in Mg2+ ion concentration and variation in pH had little effect on the apparent equilibrium constant. Mg2+ ions were necessary for the reaction. Mn2+, Co2+, Ca2+, Zn2+ and Ni2+ ions could partially replace Mg2+ ions as cofactor for the enzyme. The effects of Mg2+ ion concentration, pH and inhibitors on nucleoside diphosphokinase activity are studied. A rapid reaction occurred between adenosine diphosphate and inosine triphosphate or uridine triphosphate, whereas adenosine diphosphate and guanosine triphosphate or cytidine triphosphate reacted more slowly. Extracts were prepared from a number of plant tissues and all yielded preparations containing nucleoside diphosphokinase activity. The possible significance of the nucleoside diphosphokinase reaction in the carbohydrate metabolism of plants has been discussed.