PHOTOSYNTHETIC OXYGEN EVOLUTION - NET CHARGE TRANSIENTS AS INFERRED FROM ELECTROCHROMIC BANDSHIFTS ARE INDEPENDENT OF PROTON RELEASE INTO THE MEDIUM

The manganese containing center of the oxygen evolving complex accumul ates four oxidizing equivalents in the four stepped water oxidation cy cle. Based on experiments on electrochromic absorption transients and the reduction rate of the primary electron donor, P-680, it has been s peculated that the oscillations of these variables reflect the net cha rge of the center as calculated from the difference between electron a bstraction and proton release into the medium. We compared proton rele ase with electrochromism in thylakoids and core particles, and under v ariation of the rate of proton release. We found no equivalent of the variations of the extents and the rates of proton release in electroch romism. The oscillatory pattern of the latter reflects the topological properties of the stepped charge storage relative to the position and orientation of electrochromically responsive pigments rather than res ponding to proton release from the periphery.