BACTERIORHODOPSIN IN LANGMUIR-BLODGETT-FILMS IMAGED WITH A SCANNING TUNNELING MICROSCOPE

Mono- and bilayer Langmuir-Blodgett (LB) films of bacteriorhodopsin (b R) in an added soya phosphatidylcholine matrix were studied with scann ing tunneling microscopy (STM). Layer thicknesses of about 2.5 ran and 4.5-4.8 nm, were observed in STM images and correspond well with the length of phospholipids and bR molecules, respectively. The different layer thicknesses obtained show the existence of mono- and multilayer structures. Molecular resolution images indicate that bR protein is em bedded in the phospholipid matrix. In addition, local ordering was ima ged of bR units of about 6 nm similar to native purple membrane (PM). Intermolecular distances of 0.41 +/- 0.03 and 0.50 +/- 0.03 nm, indica ting methyl groups of phospholipids, and spacings of 0.70 +/- 0.05 and 0.65 +/- 0.10 nm, corresponding to the polar ends of phospholipids, w ere observed. Evidence of local areas of monolayers and bilayers of ba re phospholipids was found. On the basis of the results obtained by ST M imaging, a possible model is proposed for the structure of bR:soya-P C LB film.