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

Abstract

Flash-induced absorption changes in the UV have been monitored with nanosecond time resolution in oxygen-evolving photosystem II complexes from Synechococcus sp. At 260 nm, the oxidation of the immediate donor to Chl-a: (P-680+) in the l&500 ns range could be observed directly. The difference extinction coefficient for its oxidation is estimated to be 6000-8000 M-l .cm-' at 260 nm. The observed kinetics for the oxidation of the donor is identical with the reduction kinetics of Chl-a: as monitored at 824 nm. At 320 nm, the reduction of QA was found to be faster than 1 ns.

Electron-transfer events near the reaction center in oxygen-evolving photosystem II preparations

“…Leaving out heterogeneity in the manganese cluster, the scheme is linear with only Yz carrying electrons from manganese to P^o• The dependence of the electron-transfer rates on S state may be due to electrostatic effects resulting from varying charge distributions in the OEC in the different S states. Recent time-resolved optical measurements at 260 and 824 nm also support the idea that Yz is the only donor between P680 and the OEC (Gerken et al, 1987).…”

Removal of the PsaF Polypeptide Biases Electron Transfer in Favor of the PsaB Branch of Cofactors in Triton X‐100 Photosystem I Complexes from Synechococcus sp. PCC 7002†

“…The fast and slow kinetic phases of menasemiquinone oxidation were measured optically on the nanosecond time scale by monitoring the flash‐induced transient absorption change at 380 nm using a time‐resolved spectrophotometer similar to that described in Gerken et al . (22). The excitation beam was provided by a frequency‐doubled (λ = 532 nm), Q‐switched Nd:YAG laser (DCR‐11; Spectra Physics, Mountain View, CA) operated in the short pulse mode (∼3 ns).…”

Forward electron transfer from phylloquinone A1 to iron-sulfur centers in spinach photosystem I

“…Spectroscopic Measurements. Flash-induced absorbance measurements with a time resolution of 5 ns were performed with the setup described by Gerken et al (1987), using repetitive excitation (1.7 Hz) by 532-nm laser flashes of 3-ns duration, approximately 2 mJ/cm2. The bandwidth (full width at half-maximum) of the measuring beam was usually between 7 and 10 nm, except for measurements at 450 and 488 nm where it was only 3 nm.…”