LOCALIZATION OF THE OXYGEN-EVOLVING COMPLEX OF PHOTOSYSTEM-II BY FOURIER DIFFERENCE ANALYSIS

Two-dimensional (2-D) crystals of photosystem II (PSII) void of the oxygen-evolving complex (OEC) have been obtained by Tris-treatment of in-situ crystallised PSII (tPSII). The two-dimensional crystals of Tris-treated (a = 17.7 nm, b = 20.1 nm and gamma = 91 degrees) and non-Tris-treated PSII (a = 16.8 nm, b = 18.9 nm and gamma = 91 degrees) have been analyzed by electron microscopy in conjunction with image processing and Fourier difference analysis. The results (i) reveal the first assignment of three high-density regions within the boundaries of the four previously reported lumenal domains to the OEC, (ii) confirm the monomeric nature of PSII within the thylakoid membranes, and (iii) allow functional implications of the arrangement of the putative oxygen evolution enhancing (GEE) subunits to be discussed. From molecular mass estimates it is suggested, that there is only one copy of each OEE subunit per PSII complex.