RIBONUCLEOTIDE REDUCTASE FROM REGENERATING RAT LIVER

Ribonucleotide reductase was purified 150‐fold from crude extracts of 48 hour regnerating rat liver using centrifugation at 100 000 ×g, pH 5 precipitation, ammonium sulfate fractionation, and Cγ‐alumina adsorption. The enzyme activity was assayed by the conversion of [3H]cytidine nucleotides to deoxycytidine nucleotides. For optimal activity the enzyme required addition of ATP, Mg ions, Fe ions, and a dithiol reducing agent. Ribonucleotide reductase could be demonstrated in crude extracts of regenerating livers but not in livers of normal or sham operated rats. After purification, however, all three types of livers were found to contain the enzyme, regenerating livers having the highest levels. After partial hepatectomy ribonucleotide reductase activity increased approximately 20‐fold with a maximum at 50 hours after operation. Within the next 50 hours the enzyme levels decreased to those of normal liver tissue. Copyright © 1969, Wiley Blackwell. All rights reserved