Y(z)· reduction kinetics in the absence of the manganese-stabilizing protein of photosystem II

Decay of Signal II(vf) 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, ΔpsbO, which lacks the extrinsic 33 kDa manganese-stabilizing protein (MSP). Previous polarographic analysis had shown that O₂ release during the S₃→[S₄]→S₀ transition of the catalytic cycle is significantly retarded in the ΔpsbO 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 half-time of the Signal II(vf) component, corresponding to Y(z)· reduction during the S₃→[S₄]→S₀ transition, was estimated to be 1.2 and 6.0 ms in the wild-type and ΔpsbO cells, respectively.