THE ALGINATE POLYANION FACILITATES THERMAL DEACTIVATION OF PHOTOSYNTHETIC OXYGEN EVOLUTION

The effects of the alginate polyanion on photosynthetic O-2 evolution by spinach thylakoid membrane fragments and photosystem II particles w ere examined. Contrary to what would be expected for a ''thickening ag ent'' alginate was found to intensity the thermal inactivation of phot osynthetic O-2 evolution. Isolated photosystem II particles were subst antially more susceptible to alginate-promoted thermal inactivation th an thylakoids. This suggests direct interaction of the polyanion with the O-2-evolving complex as the inactivation cause in view of the fact that the polyanion can access the complex only in photosystem II part icles but not in sealed thylakoid vesicles. However, long-range effect s on O-2 evolution, caused by the interaction of alginate with the out er thylakoid surface, are also possible. The alginate-promoted inactiv ation of the O-2-evolving complex was not related to the dissociation of the extrinsic proteins since Ca2+ and Cl- ions could not reactivate inactive photosystem II particles. Glycine betaine, a stabilizer of t he higher order structure of the O-2-evolving complex, was found capab le of counteracting the destabilizing effects of alginate.