Ribonucleotide Reductase—a Radical Enzyme

Abstract

Ribonucleotide reductases catalyze the enzymatic formation of deoxyribonucleotides, an obligatory step in DNA synthesis. The native form of the enzyme from Escherichia coli or from mammalian sources contains as part of its polypeptide structure a free tyrosyl radical, stabilized by an Fe center. The radical participates in all probability in the catalytic process during the substitution of the hydroxyl group at C-2 of ribose by a H atom. A second, inactive form of the E. coli reductase lacks the tyrosyl radical. Extracts from E. coli contain activities that interconvert the 2 forms. The tyrosyl radical is introduced in the presence of O2, while anaerobiosis favors its removal, suggesting a regulatory role in DNA synthesis for O2.