Purification and Properties of Ribonucleotide Reductase from Leukemic Mouse Spleen

A 13-fold increase was observed in the specific activity of ribonucleotide reductase activity in the spleen of mice infected with a murine leukemia virus. After partial purification, the properties of the enzyme were investigated. The pH optimum was between 6.8 and 7.4. There was an absolute requirement for a hydrogen donor, dithiothreitol. Magnesium ions stimulated the reaction. The ribonucleoside diphosphates were the preferred substrates. The reduction rate was affected by the presence of nucleoside triphosphates in concentrations ranging from 5 x 10-5 to 10-3 m. The reduction of CDP was stimulated by dCTP and ATP. UDP reduction was stimulated by ATP. The reduction of ADP was stimulated by GTP and dGTP. The GDP reduction was stimulated by dTTP. In the presence of ATP, the weak activators, dTTP and dATP, inhibit the CDP reduction. With minor exceptions, the ribonucleotide reductase from murine leukemic spleen closely resembles that of Novikoff hepatoma.