A high-field EPR tour of radicals in photosystems I and II

High magnetic-field electron paramagnetic resonance (HFEPR) has been extensively applied to the study of photosynthetic reaction centers. HFEPR experiments have provided accurate measurements of g-values of radicals in photosystems I and II. The g-values not only reflect the structure of the radical, but also its immediate environment. Hence, valuable information about radical-protein interactions can be obtained from g-values. Data on tyrosine-, quinone-, pheophytin- and chlorophyll-based radicals are reviewed. Experiments dealing with spin pairs in photosystem I and 11 are examined. The spectrometer with which numerous experiments on photosystems have been carried out is described, as well as the 10 T magnet around which the spectrometer is based.