Catalytic center of oxygen-evolving complex (OEC) of photosystem II (PSII) is Mn4CaO5 cluster structure of which is determined now. Ca2+ extraction from OEC is accompanied by decoupling of oxygen evolution and electron transport processes in PSII and by the appearance of a broad EPR signal (so-called “S3” or “split signal”) at low temperatures. These data imply that decoupling and EPR effects can be interdependent. It is interesting that EPR signal «S3» is observed also after treatment of native PSII membranes by fluoride anions, acetate and chloride of ammonia. Previously we found that fluoride anions treatment of PSII like Ca2+ extraction from the OEC provide the appearance of decoupling effect. In the presented work we investigated the effect of ammonia chloride and ammonia nitrate on the functional activity of native PSII membranes to study the effect of anions. We found that ammonia nitrate like ammonia chloride inhibit the oxygen evolution more effectively than the reduction of artificial electron acceptor 2,6- dichlorophenolindophenol that is the action of ammonia decouples these processes. However the inhibition doesn’t depend on the anions. We suggest that ammonia inhibition effect is determined by inactivation of Ca2+ function.
photosystem II, oxygen-evolving complex, ammonia
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