X-RAY REFLECTIVITY ANALYSIS OF LANGMUIR-BLODGETT-FILMS OF REACTION-CENTER PROTEINS FROM PHOTOSYNTHETIC BACTERIA

Langmuir-Blodgett (LB) films of the reaction center protein-pigment co mplexes (RCs) isolated from photosynthetic bacteria Chloroflexus auran tiacus,, Rhodobacter sphaeroides and Rhodopseudomonas viridis were pre pared and investigated by small-angle X-ray reflectivity. The patterns obtained for the eight-monolayer (LB) films of the RCs from Rb. sphae roides and Rps. viridis show well defined Kiessig fringes. This confir ms the preparation of molecularly smooth (roughness less than 1.5 nm), flat RC films and allows us to estimate their thickness as 30.5 and 3 4.0 nm respectively. Well ordered RC deposition took place only onto t he ''front'' side of the substrate, which faces the moving barrier in the Langmuir trough. X-ray reflectivity measurements of LB films of RC s from C. aurantiacus show no Kiessig fringes, independent of the side of the glass plate; this can be explained due to the formation of an unordered protein film during LB deposition. These effects are due to the high asymmetry of the RCs from Rb. sphaeroides and, especially, Rp s. viridis in comparison with the RCs from C. aurantiacus.