A. Graslund et M. Sahlin, ELECTRON-PARAMAGNETIC-RESONANCE AND NUCLEAR-MAGNETIC-RESONANCE STUDIES OF CLASS-I RIBONUCLEOTIDE REDUCTASE, Annual review of biophysics and biomolecular structure, 25, 1996, pp. 259-286
Ribonucleotide reductase catalyses the reduction of ribonucleotides to
the corresponding deoxyribonucleotides needed for DNA synthesis. This
review describes recent studies on the iron/tyrosyl free radical site
in the R2 protein of iron-containing (class I) ribonucleotide reducta
ses. The active enzyme is composed of two homodimeric proteins, R1 and
R2. Active protein R2 contains a diiron-oxygen site and a neighboring
free radical on a tyrosyl residue per polypeptide chain. The properti
es of the different redox states of the diiron center in protein R2 ar
e discussed, as well as the formation of the iron/radical site and its
possible involvement in long range electron transfer from the substra
te binding site in protein R1. The EPR properties of oxidized neutral
tyrosyl free radicals are described, and also of tryptophan free radic
als found in studies of a mutant of the R2 protein, which lacks the ty
rosyl radical site. NMR studies on protein R2 include observations of
paramagnetically shifted resonances. Structural NMR studies have been
performed on its highly mobile C-terminal domain as well as the corres
ponding oligopeptide which interacts with protein R1.