ANOTHER ROLE OF CHLOROPHYLL a/b BINDING PROTEINS OF HIGHER PLANTS: THEY MODULATE PROTOLYTIC REACTIONS ASSOCIATED WITH PHOTOSYSTEM II

Chlorophyll alb binding proteins serve as light-harvesting antennae. Additionally they seem to modulate proton pumping by photosystem II, because their covalent modification by N, N-dicyclohexylcarbodiimide is paralleled by a short-circuit of this activity. This side action was further characterized in comparative study with control thylakoids and thylakoids lacking chlorophyll alb binding proteins. The latter were derived from peas grown under intermittent light. They differed from controls in the following: (i) after incubation with A^A^-dicyclohexylcarbodiimide there was no protonic short circuit, (ii) under flashing light the rate of proton consumption at the acceptor side of photosystem II was accelerated and (iii) the periodical pattern of proton release from water oxidation was flattened out. It was obvious that chlorophyll alb binding proteins modulated the kinetics and the stoichiometry of proton release from water oxidation and proton uptake at the quinone binding pocket.