SINGLE-MOLECULE HIGH-RESOLUTION STRUCTURE AND ELECTRON CONDUCTION OF PHOTOSYSTEM-II FROM SCANNING-TUNNELING-MICROSCOPY AND SPECTROSCOPY

Scanning tunneling microscopy (STM) and spectroscopy (STS) were used t o obtain the first direct high resolution (similar to 0.3 nm) images o f single isolated Photosystem II (PS II) molecules, and to determine t he supramolecular organization of oxygen-evolving PS II core complexes and PS II membrane fragments including the identification, assignment , location and dimensions of the polypeptide units. Our results predic t a unique structural model which we then compare with alternative mod els. We show that the combination of quasi-constant-height mode STM op eration, STS and suitable choice of sample-substrate preparations can be used to enable investigation of the structure and function of singl e PS II particles under normal thermodynamic and hydration conditions without the requirement and complications of ordered PS II arrays or c rystals. STS was also used to characterize single-molecule electron co nduction and tunneling mechanisms in PS LI including the semiconductio n and photoconduction behavior of the reaction center and photoexcitat ion effects in the light-harvesting complex LHC II. (C) 1998 Elsevier Science B.V. All rights reserved.