Monolayer characteristics of bacterial photosynthetic reaction centers

Abstract

Monolayers of the reaction center protein—pigment complexes, isolated from photosynthetic bacteria Chloroflexus aurantiacus, Rhodobacter sphaeroides (wild type and strain R-26) and Rhodopseudomonas viridis were prepared at air/aqueous solution interfaces. The surface pressure—area isotherms of these proteins were determined at various ionic strengths, pH and temperatures of the aqueous subphase to establish optimum conditions for stable film preparations: 10 mM phosphate buffer as the liquid subphase at pH 7.0 and 20°C. At these conditions the maximal collapse areas per reaction center complex from Rb. sphaeroides (both types have three protein subunits) and C. aurantiacus (two subunits) are in the range 35–45 nm 2, while from R. viridis (four subunits) the area is about 90 nm 2. Monolayers were transferred to roughened Ag electrodes for recording surface-enhanced resonance Raman scattering (SERRS) spectra at two excitation wavelengths (406.7 and 488.0 nm).