INVESTIGATION OF INTERACTION FE-57(3-BINDING SITE OF PHOTOSYNTHETIC OXYGEN-EVOLVING COMPLEX OF PSII() WI TH CA2+)

The oxygen-evolving PSII membranes (I) and the Ca2+-depleted PSII memb ranes (II) were incubated in (FeCl3)-Fe-57-sucrose solution and their Mossbauer spectra were registered. Spectrum of resonance absorption of these samples displayed analogous shape; the value of effect indicate d a high level of the unspecifically bound Fe-57(3+). Parameters of ch emical shift (delta) and quadrupole splitting (Delta) of the iron ion were delta = 0.38 mm/s, Delta = 0,76 mm/s. After removal of the unspec ifically bound Fe-57(3+) by o-phenanthroline, the Mossbauer spectra of the PSII membranes (I) represented superposition of three doublets; t he spectra or the Ca2+-extracted PSII membranes (II) displayed four do ublers. The relative content of the 4th component was 43%. The appeara nce of the 4th component in the spectra of the Ca2+-depleted PSII memb ranes (II) can be explained by substitution of Ca2+ by Fe3+ in the Ca2 +-bounding site.