Ribonucleotide reductase which can reduce physiological and pharmacological diphosphate compounds, exhibits wide substrate specificity. Furthermore, the enzyme exhibits complex regulatory properties. Ribonucleotide reduc is reguated allosterically by many purine and pyrimidine nucleotides; this regulation is quite intricate and is designed to maintain appropriate concentrations of the deoxyribonucleotides for DNA synthesis. dATP serves as an allosteric inhibitor for the reduction of all nucleoside diphosphates.