Ribonucleotide reductase (RNR), also known as ribonucleoside diphosphate reductase, is an enzyme that catalyzes the formation of deoxyribonucleotides from ribonucleotides.[1][2] It catalyzes this formation by removing the 2'-hydroxyl group of the ribose ring of nucleoside diphosphates (or triphosphates depending on the class of RNR). This reduction produces deoxyribonucleotides.[3] Deoxyribonucleotides in turn are used in the synthesis of DNA. The reaction catalyzed by RNR is strictly conserved in all living organisms.[4] Furthermore, RNR plays a critical role in regulating the total rate of DNA synthesis so that DNA to cell mass is maintained at a constant ratio during cell division and DNA repair.[5] A somewhat unusual feature of the RNR enzyme is that it catalyzes a reaction that proceeds via a free radical mechanism of action.[6][7] The substrates for RNR are ADP, GDP, CDP and UDP. dTDP (deoxythymidine diphosphate) is synthesized by another enzyme (thymidylate kinase) from dTMP (deoxythymidine monophosphate).
^Eklund H, Eriksson M, Uhlin U, Nordlund P, Logan D (August 1997). "Ribonucleotide reductase—structural studies of a radical enzyme". Biological Chemistry. 378 (8): 821–5. doi:10.1515/bchm.1997.378.8.815. PMID9377477.
^Stubbe J, Riggs-Gelasco P (November 1998). "Harnessing free radicals: formation and function of the tyrosyl radical in ribonucleotide reductase". Trends in Biochemical Sciences. 23 (11): 438–43. doi:10.1016/S0968-0004(98)01296-1. PMID9852763.