Ribonucleotide ReducÃ-aseActivity in Cell-free Extracts of Yaba Poxvirus Tumor and Normal Monkey Tissues1

Ribonucleotide reductase activity in cell-free tissue extracts from Yaba monkey tumors, spleen, kidney, liver, and muscle has been measured in vitro. The specific activity of the enzyme in the Yaba tumor extracts was approximately two times that observed in normal muscle tissue extracts and ten times that in normal liver, spleen and kidney extracts. The specific activity in Yaba tumor extracts does not show an absolute requirement for ATP although the presence of exogenous ATP increases enzyme activity. A loss in specific activity occurs after dialysis of the Yaba tumor extracts but not with the extracts from normal monkey spleen. Ribonucleotide reductase activity from Yaba tumor extracts is inhibited by exogenous deoxyadenosine 5'-triphosphate, deoxycytidine 5'-triphosphate, and deoxyguanosine 5'-triphosphate ; it is inhibited slightly by deoxythymidine 5'-triphosphate.