A resonance Raman investigation of the effect of lithium dodecyl sulfate on the B800–850 light-harvesting protein of Rhodopseudomonas acidophila 7750

Abstract

The effect of the detergent lithium dodecyl sulfate (LDS) on the resonance Raman spectrum of the carotenoid and bacteriochlorophyll in the B800–850 light-harvesting complex Rhodopseudomonas acidophila 7750 was determined. Treatment of B800–850 complex with 0.1% LDS resulted in a 3 cm −1 downshift of the carotenoid v 3 Raman band, a 2 cm −1 upshift of the carotenoid v 1 band, with no change in the v 2. This indicates that LDS treatment induces a 7- cis-isomerization of the carotenoid and a supplementary torsion of the polyene chain around the C(8)–C(9) bond. Also, treatment of B800–850 complex with LDS resulted in several changes attributable to alterations in the nature of the binding to the protein of the acetyl and keto-carbonyls of one bacteriochlorophyll. No change was observed in the coordination of the bacteriochlorophyll central magnesium. These data indicate that the 800 nm-absorbing bacteriochlorophyll remains bound to the protein upon LDS treatment. The resonance Raman data indicate that the pronounced absorption spectral changes reported previously (Chadwick, B.W., Zhang, C., Cogdell, R.J. and Frank, H.A. (1987) Biochim. Biophys. Acta 893, 444–451) are attributable to a dramatic perturbation of the protein environment upon LDS treatment of the B800–850 complex.