PROTON RELEASE FROM WATER OXIDATION BY PHOTOSYSTEM-II - SIMILAR STOICHIOMETRIES ARE STABILIZED IN THYLAKOIDS AND PSII CORE PARTICLES BY GLYCEROL

During the four-stepped catalytic cycle of mater oxidation by photosys tem II (PSII) molecular oxygen is released in only one of the four rea ction steps whereas the release of four protons is distributed over al l steps, In principle, the pattern of proton production could be taken as indicative of the partial reactions with bound water, In thylakoid s the extent and rate of proton release varies as function of the redo x transition and of the pH without concomitant variations of the redox pattern, The variation has allowed to discriminate between deprotonat ion events of peripheral amino acids (Bohr effects) as opposed to the chemical deprotonation of a particular redox cofactor, and of water, T n contrast, in thylakoids grown under intermittent light, as web as in PSTI core particles the pattern of proton release is flat and indepen dent of the pH. This has been attributed to the lack in these material s of the chlorophyll a,b-binding (CAB) proteins, We now found that a t hylakoid-like, oscillatory pattern of proton release was restored simp ly by the addition of glycerol which modifies the protein-protein inte raction, Being a further proof for the electrostatic origin of the gre ater portion of proton release, this effect will serve as an important tool in further studies of water oxidation. (C) 1997 Federation of Eu ropean Biochemical Societies.