Y-Z(CENTER-DOT) REDUCTION KINETICS IN THE ABSENCE OF THE MANGANESE-STABILIZING PROTEIN OF PHOTOSYSTEM-II

Decay of Signal IIvf of photosystem II (PSII), under repetitive flash conditions, was examined in whole cells of wild-type Synechocystis sp. PCC6803 and in cells of an engineered strain, Delta psbO, which lacks the extrinsic 33 kDa manganese-stabilizing protein (MSP). Previous po larographic analysis had shown that O-2 release during the S-3-->[S-4] -->S-0 transition of the catalytic cycle is significantly retarded in the Delta psbO strain relative to the wild-type [Burnap et al. (1992) Biochemistry 31, 7404-7410]. The present experiments provide evidence that a parallel retardation in the rate of reduction of photooxidized Y-z by the H2O oxidation complex is due to the absence of MSP. The hal f-time of the Signal IIvf component, corresponding to Y-z(.) reduction during the S-3-->[S-4]-->S-0 transition, was estimated to be 1.2 and 6.0 ms in the wild-type and Delta psbO cells, respectively.