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 higher plant photosystem II (PSII) by various salt-washing procedures has 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 of two-dimensional (2-D) crystals of PSII. In addition to the previously characterised 2-D crystals of native PSII and Tris-washed PSII, we report 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=89 degrees). The three extrinsic subunits were mapped to three separate locations on the lumenal side of the complex. The structural information derived from these studies is discussed in the light of recent crosslinking and other biochemical investigations allowing a further exploration of the relationships between PSII architecture and photosynthetic oxygen evolution. Copyright (C) 1996 Elsevier Science Ltd.