Proton and electron transfer in the acceptor quinone complex of photosynthetic reaction centers from Rhodobacter sphaeroides.

For twenty years the photosynthetic reaction center (RC) has been the premier testing ground for theoretical understanding of electron transfer in aperiodic systems, with special, but not unique, reference to long distance biological electron transport. In addition to the known structure, many of the attributes that make RCs so well suited to studying electron transfer function equally well for any charge movement, including protons. These include the presence of intrinsic reporter groups (electrochromically active pigments), high time resolution through light activation, and a large number and variety of distinct reactions, ranging from loosely coupled responses of the protein dielectric to specific, long distance proton transfers in and out of active sites, and bond making in terminal chemical transformations. A wide variety of biophysical methods have been coupled with site directed mutagenesis to reveal mechanisms of proton uptake, transfer and chemistry in the RC. This review summarizes our progress to date, which suggests that the RC can serve as a paradigm, not only for many energy coupled, membrane proteins, but for the electrostatic and dielectric properties of proteins that are critical to their general function.