Ribonucleotide reductase which can reduce c physiological and pharmacological diphosphate w compounds, exhibits wide substrate specificity. d Furthermore, the enzyme exhibits complex regula- v tory properties. Ribonucleotide reduc is regu- c ated allosterically by many purine and pyrimidine al nucleotides; this regulation is quite intricate and is es designed to maintain appropriate concentrations of hy the deoxyribonucleotides for DNA synthesis. dATP en serves as an allosteric inhibitor for the reduction of all nucleoside diphosphates.