An iron-dependent 5'-nucleotide phosphoribohydrolase activity in the venom of Crotalus atrox and its effect upon the determination of mammalian ribonucleotide reductase.

There is an iron-dependent activity in the venom of Crotalus atrox which appears to hydrolyze the N-glycosidic sugar-base bond of pyrimidine and purine nucleotides. Maximal activation of this activity occurred at 1.0 mmol/l and 0.8 mmol/l FeCl3 for cytidine diphosphate (CDP) and ADP substrates, respectively. The release of free base affects the background values of control experiments carried out during nucleotide-labelled assays of ribonucleotide reductase which require the conversion of nucleotides to nucleosides by snake venom treatment. When the reductase is examined in intact cells, a situation closely resembling normal physiological conditions for the enzyme, FeCl3 was found to be an inhibitor of ADP reductions and varied from a mild stimulator to a significant inhibitor of CDP reductions depending upon FeCl3 concentration. Possible explanations for previously observed variability in ribonucleotide reductase activity in the presence of iron are suggested.