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Abstract— It appears that even if some kinetic aspects of the activation and stimulation phenomena of photosystem II remain not understood. the only interpretation we can propose involves the addition of the effect of two photoreactions on the same photochemical center. The main arguments we developed in favour of this hypothesis are: (1) the formation of one atom of oxygen requires the addition of the effect of two photo‐reactions (one photoreaction per electron). (2) after a dark period two quanta must be absorbed by the same photochemical center in order to produce oxygen. (3) the existence of a form of the photochemical substrate in which energy is stored is proved by the fact that. after a preillumination by two flashes, the quantum requirement for the production of one molecule of oxygen can reach a value almost two times lower than the quantum requirement measured in stationary conditions.
Pierre Joliot (Fri,) studied this question.