Kinetic evidence for the function of Z in isolated photosystem II reaction centers

(D1,D2) Photosystem II reaction centers were studied by flash absorption spectroscopy with microsecond resolution. Without addition, absorption transients in the 660–850 nm region are due to a triplet state, probably of P‐680, with a decay half‐time of 700 μs (no oxygen) or 40 μs (under air). With the addition of DBMIB, presumably acting as electron acceptor, new kinetic and spectral features appear, which are attributed to P‐680. A 5 μs phase of decay is present, which is pH‐dependent and is attributed to donation from Z to P‐680+.