A near infrared electronic transition associated with conversion between S‐states of the photosynthetic O2‐evolving complex

Abstract

A new electronic transition is observable in O2‐evolving photosynthetic membranes of spinach enriched in Photosystem II. The transition occurs predominantly in the oxidation state created after a single flash of light (S2 state). It oscillates in yield with a period of flashes when exposed to a train of short light flashes. Conditions which abolish O2 evolution and remove functional manganese destroy this effect. The spectrum and absorptivity of the oscillating component are similar to those found in synthetic manganese dimers poised in the mixed‐valent oxidation state Mn2(III,IV). A similar structural unit is thus implicated for the manganese site involved in O2 evolution.