Direct observation of the immediate electron donor to chlorophyll- a+II(P-680 +) in oxygen-evolving photosystem II complexes Resolution of nanosecond kinetics in the UV

Flash-induced absorption changes in the UV have been monitored with nanosecond time resolution in oxygen-evolving photosystem II complexes from Synechococcussp. At 260 nm, the oxidation of the immediate donor to Chl- a+II(P-680 +) in the 10–500 ns range could be observed directly. The difference extinction coefficient for its oxidation is estimated to be 6000–8000 M −1·cm −1at 260 nm. The observed kinetics for the oxidation of the donor is identical with the reduction kinetics of Chl- a+IIas monitored at 824 nm. At 320 nm, the reduction of Q Awas found to be faster than 1 ns.