UV‐spectral characterization in Tris‐washed chloroplasts of the redox component D₁which functionally connects the reaction center with the water‐oxidizing enzyme system Y in photosynthesis

Amplitude and relaxation kinetics of UV‐absorption changes induced in Tris‐washed chloroplasts by the second flash of repetitive double flash groups were found to be dependent on the time between the flashes of each group. An analysis of these data leads to the conclusion that after oxidation by P680 + the donor component, D ox 1 , becomes mainly reduced by the primary (Q − A ) and secondary (Q − B ) plastoquinone in non‐B‐type and B‐type system II centers, respectively. D ox 1 reduction with Q − A occurs with t 1/ = 60–100 ms, and D ox 1 reduction with Q − B is biphasic with half‐times of 0.1–0.5 and 5–10 s. The difference spectrum of the oxidized vs reduced form of D 1 is presented in the range 250–370 nm. It is characterized by positive bands peaking at 265–270 and 300–305 nm with a smaller band around 350 nm; negative bands are not observed.