Extrinsic polypeptides of the chloroplast oxygen evolving complex constitute the tetrameric ESs particles of higher plant thylakoids

Abstract

Inside-out vesicles derived from grana partition regions of spinach thylakoids were isolated by Yeda press treatment followed by aqueous polymer phase partitioning. Their structure was examined by freeze-etch electron microscopy, which revealed numerous tetrameric particles on their outer surface, corresponding to the ESs particles of the lumenal surface of intact thylakoids. The vesicles were treated with several different salt washes which specifically removed some or all of the extrinsic polypeptides of the oxygen evolving complex. Removal of the 16 and 23 kD extrinsic polypeptides with NaCl caused a reduction in the surface relief or loss of the tetrameric structure of the ESs particles. When the 33 kD polypeptide was removed in addition to the 16 and 23 kD polypeptides, either by washing with CaCl2 or alkaline Tris, the particles could no longer be clearly resolved from the membrane surface. Vesicles washed with 1m-CaCl2 were reconstituted with a 10-fold excess of a crude extract containing the extrinsic polypeptides of the oxygen evolving complex. This resulted in the reappearance of particles on the membrane surface, although they did not have a clear tetrameric structure. Thus the extrinsic polypeptides of the oxygen evolving complex are the major components of the tetrameric ESs particles of thylakoids.