title: Effect of the redox state of QB on electric field-induced charge recombination in Photosystem II.
abstract: Electric field-induced charge recombination in Photosystem II (PS II) was studied in osmotically swollen spinach chloroplasts ('blebs') by measurement of the concomitant chlorophyll luminescence emission (electroluminescence). A pronounced dependence on the redox state of the two-electron gate QB was observed and the earlier failure to detect it is explained. The influence of the QB/QB (-) oscillation on electroluminescence was dependent on the redox state of the oxygen evolving complex; at times around one millisecond after flash illumination a large effect was observed in the states S2 and S3, but not in the state 'S4' (actually Z(+)S3). The presence of the oxidized secondary electron donor, tyrosine Z(+), appeared to prevent expression of the QB/QB (-) effect on electroluminescence, possibly because this effect is primarily due to a shift of the redox equilibrium between Z/Z(+) and the oxygen evolving complex.
authors.affiliation: Department of Biophysics, Huygens Laboratory of the State University, Leiden, P.O. Box 9504, 2300 RA, Leiden, The Netherlands.
authors.forename: P W
authors.initials: PW
authors.lastname: Hemelrijk
authors.forename: H J
authors.initials: HJ
authors.lastname: van Gorkom