Evidence for the electrochromic identification of the change of charges in the four oxidation steps of the photoinduced water cleavage in photosynthesis

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Abstract
After dark adaptation of oxygen‐evolving photosystem (PS) II complexes, oscillatory absorption changes (stable >0.5 s) with a period of 4 were previously detected at 514 nm, probably due to electrochromic band shifts of carotenoids [(1984) FEBS Lett. 176, 83‐87]. To support this interpretation, we looked for corresponding phenomena in the 650–714 nm range. Here, oscillations were also observed with a difference spectrum giving evidence for an electrochromic band shift of the chlorophyllaabsorption band. The oscillation pattern 0:0:+:+ corresponds to those at 514 nm, supporting the former conclusion that the states S2and S3have a surplus charge compared to S0and S1. This is possible if the electron release pattern 1:1:1:1 is accompanied by an intrinsic proton release pattern 1:0:1:2 for the transition S0→ S1→ S2→ S3→ S0.