Manganese and tyrosyl radical function in photosynthetic oxygen evolution

Abstract Photosystem II catalyzes the photosynthetic oxidation of water to O 2 . The structural and functional basis for this remarkable process is emerging. The catalytic site contains a tetramanganese cluster, calcium, chloride and a redox-active tyrosine organized so as to promote electroneutral hydrogen atom abstraction from manganese-bound substrate water by the tyrosyl radical. Recent work is assessed within the framework of this model for the water oxidizing process.