The conformational stability of bacteriochlorophyll—Protein complex isolated from a green photosynthetic bacterium: II. The action of detergents on the bacteriochlorophyll-protein complex

Abstract

The interactions of anionic, cationic, and nonionic detergents with bacteriochlorophyll-protein (Bchl-P) 3 3 The following abbreviations are used: Bchl-P, bacteriochlorophyll-protein; Bph-P, bacteriopheophytin-protein; Bchl, bacteriochlorophyll; Bph, bacteriopheophytin; SDS, sodium dodecyl sulfate; SDBS, sodium dodecyl benzene sulfonate; HTAB, hexadecyl trimethyl ammonium bromide; Triton X-100, isooctyl phenoxy polyethoxy ethanol; THAM, tris (hydroxymethyl) amino methane; ORD, optical rotatory dispersion; CD, circular dichroism. complex isolated from a green photosynthetic bacterium Chloropseudomonas ethylicum have been examined. The effects of the detergents on the Bchl-P complex have shown a considerable variation depending on the type of the polar head-group and the nonpolar group of the detergent molecules. The anionic detergents, sodium dodecyl sulfate and sodium dodecyl benzene sulfonate, acting on Bchl-P, separate bacteriochlorophyll from the protein moiety and pheophytinize the Bchl by ligand bonding interaction. Pure Bchl is also converted into bacteriopheophytin by SDS. The interaction of a cationic or nonionic detergent with Bchl does not produce Bph. The Bchl-P complex is dissociated into Bchl and protein component by the cationic detergent, HTAB, or by a mixed solution of non-ionic detergent, Triton X-100, and 8 m urea. The ORD spectrum of Bchl-P in the uv range suggests that a significant change in protein conformation has taken place as a result of the detergent actions. Probable mechanisms for the combined action of Triton and urea on the complex are discussed.