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 ox ygen-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 b een analyzed by electron microscopy in conjunction with image processi ng and Fourier difference analysis. The results (i) reveal the first a ssignment of three high-density regions within the boundaries of the f our previously reported lumenal domains to the OEC, (ii) confirm the m onomeric nature of PSII within the thylakoid membranes, and (iii) allo w functional implications of the arrangement of the putative oxygen ev olution enhancing (GEE) subunits to be discussed. From molecular mass estimates it is suggested, that there is only one copy of each OEE sub unit per PSII complex.