Ribonucleotide reductase: Kinetic methods for demonstrating radical transfer pathway in protein R2 of mouse enzyme in generation of tyrosyl free radical

Abstract

Ribonucleotide reduction is necessary for the biosynthesis of the deoxyribonucleotides needed for DNA synthesis and repair. The conversion to deoxyribonucleotides from the corresponding ribonucleotides is strictly regulated throughout the cell cycle, and this reaction may be regarded as a bottleneck for cell proliferation. Ribonucleotide reductase (RNR) [ribonucleotide-diphosphate reductase] catalyzes the reduction of ribonucleotides. At least three different classes of ribonucleotide reductases have been described. They all use metals and free radical chemistry for the seemingly simple reaction to reduce the T-hydroxyl group in the ribose ring. The iron-containing class I ribonucleotide reductases (RDR) contain a tyrosyl free radical in their active state. The substrates for RDR are the nucleoside diphosphates. RDR is found, e.g., in mammalian cells as well as in aerobically growing Escherichia coli and is coded for by certain viruses.