REGULATION OF XANTHINE DEHYDROGENASE IN CHICK LIVER. EFFECT OF STARVATION AND OF ADMINISTRATION OF PURINES AND PURINE NUCLEOSIDES

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Abstract
The xanthine-dehydro-genase activity of chick liver, expressed per mg N increased during starvation. Administration of inosine and possibly of adenine had a comparable effect on the xanthine dehydrogenase, and also induced an elevation of the total quantity of enzyme. Hypoxanthine, xanthine, gua-nine, xanthosine, guanosine and adenosine were ineffective. Cortisone was equally ineffective. The administration of puromycin abolished the effect of inosine and reduces that of starvation. Inosine induced increased synthesis of xanthine dehydrogenase, whereas during starvation the enzyme was spared with respect to other liver proteins. The hypothesis was formulated that chick-liver xanthine dehydrogenase is an adaptive enzyme, its activity being regulated by inosine or by one of its metabolites.