title: Studies on the protolytic reactions coupled with water cleavage in photosystem II membrane fragments from spinach.
abstract: The protolytic reactions of PSII membrane fragments were analyzed by measurements of absorption changes of the water soluble indicator dye bromocresol purple induced by a train of 10 μs flashes in dark-adapted samples. It was found that: a) in the first flash a rapid H(+)-release takes place followed by a slower H(+)-uptake. The deprotonation is insensitive to DCMU but is completely eliminated by linolenic acid treatment of the samples; b) the extent of the H(+)-uptake in the first flash depends on the redox potential of the suspension. In this time domain no H(+)-uptake is observed in the subsequent flashes; c) the extent of the H(+)-release as a function of the flash number in the sequence exhibits a characteristic oscillation pattern. Multiphasic release kinetics are observed. The oscillation pattern can be satisfactorily described by a 1, 0, 1, 2 stoichiometry for the redox transitions Si → Si+1 (i=0, 1, 2, 3) in the water oxidizing enzyme system Y. The H(+)-uptake after the first flash is assumed to be a consequence of the very fast reduction of oxidized Q400(Fe(3+)) formed due to dark incubation with K3[Fe(CN)6]. The possible participation of component Z in the deprotonation reactions at the PSII donor side is discussed.
authors.affiliation: Max Volmer Institut für Biophysikalische und Physikalische Chemie der Technischen Universität, Straße des 17, Juni 135, D 1000, Berlin 12, FRG.
authors.forename: G
authors.initials: G
authors.lastname: Renger
authors.forename: U
authors.initials: U
authors.lastname: Wacker
authors.forename: M
authors.initials: M
authors.lastname: Völker