Radical initiation in the class I ribonucleotide reductase: Long-range proton-coupled electron transfer?

The current understanding of the mechanism of long-range electron transfer (ET) and proton-coupled electron transfer (PCET) in biology is reviewed using the radical initiation process of class I RNRs as a focal point. An introduction to the class I RNRs is given first. Following this, the theoretical framework for ET and PCET is presented. Insight from the extensive investigations of biological systems, including, hole migration in DNA, PCET in photolyases, and ET and PCET in the photosynthetic reaction is outlined. Finally, postulated mechanisms for the radical initiation process for RNR are highlighted.