HIGH-SPECIFIC BINDING OF FE(II) AT THE MN-BINDING SITE IN MN-DEPLETEDPSII MEMBRANES FROM SPINACH

The interaction of Fe(II) and Fe(III) with the 'high-affinity Mn-bindi ng site' in Mn-depleted photosystem II (PSII) was investigated using d iphenilcarbazide (DPC)/2, 6-dichlorophenol-indophenol (DCIP) inhibitio n assay. Fe(III) was ineffective in the inhibition of DPC-DCIP reactio n while Fe(II) decreased the rate of DCIP photoreduction supported by DPC in the same concentration range as Mn(II). The effectivity of the interaction of Fe(II) with the high affinity Mn-binding site depends o n different anions in the same manner as for Mn(II) and coincides with hierarchy observed for the stimulation of O-2 evolution. The Fe(II) b inding is accompanied by its oxidation. By using reductants it was sho wn that the high affinity site contains a redox-active component and t he reduction of this component totally prevents the binding of Fe(II).