Insights into the structure and function of redox-active tyrosines from model compounds

Redox-active tyrosine residues play important roles in long distance electron-transfer reactions in enzymes, including prostaglandin H synthase, ribonucleotide reductase, and photosystem II. In cytochrome c oxidase, a cross-linked tyrosine-histidine cofactor has been proposed to play a role in proton and electron transfer reactions. Studies of tyrosyl radicals in model compounds, generated by UV photolysis, have recently provided new information about the structure and function of these redox-active species. The results of these studies, which combine magnetic resonance and optical spectroscopies, are described in this review.