PHOTOSYSTEM-II - MAPPING THE LOCATIONS OF THE OXYGEN EVOLUTION-ENHANCING SUBUNITS BY ELECTRON-MICROSCOPY

Sequential removal of the 33-, 23-, and 16-kDa extrinsic subunits of h igher plant photosystem II (PSII) by various salt-washing procedures h as been monitored by gel electrophoresis and oxygen evolution activity measurements. Structural changes induced by the subunit removal were followed by electron microscopy in conjunction with image processing o f two-dimensional (2-D) crystals of PSII. In addition to the previousl y characterised 2-D crystals of native PSII and Tris-washed PSII, we r eport 2-D crystals of 0.25MNaCl-washed (a=18.2nm, b=20.3 nm with gamma =89 degrees) and 1 MNaCl-washed PSII (a=18.2 nm, b=20.4mm with gamma=8 9 degrees). The three extrinsic subunits were mapped to three separate locations on the lumenal side of the complex. The structural informat ion derived from these studies is discussed in the light of recent cro sslinking and other biochemical investigations allowing a further expl oration of the relationships between PSII architecture and photosynthe tic oxygen evolution. Copyright (C) 1996 Elsevier Science Ltd.