The object of this study of the photosynthetic reaction center structure is to establish the molecular basis for its function in solar energy conversion. This involves an investigation of the natue of the binding site for cytochrome on the reaction center using site specific mutagenesis and the realtionship between reaction centers in bacteria and the ones in Photosystem II. Photosynthesis is the process used by plants and photosynthetic bacteria to convert sunlight into chemical energy. This process involves light initiated electron transfer reactions which takes place in a protein complex called the reaction center which is a membrane bound bacteriochlorophyII-protein complex. The reaction centers from photosynthetic bacteria have been extensively studied and well characterized by a variety of biophysical and structural techniques including X-ray crystallography which have opened up new areas of research.