The interaction of surfactants with the chloroplast thylakoid membrane at sub-solubilizing concentrations

Abstract

The interactions of nonionic, anionic and zwitterionic surfactants with the chloroplast thylakoid membrane of wheat ( Triticum aestivum) were examined. Measurements of the surface tension of the solution and behavior of the membrane material during centrifugation were used to identify solubilizing concentrations of the surfactants. Studies at sub-solubilizing concentrations indicated that the primary interaction between the surfactant and the thylakoid membrane may involve adsorption at the membrane / solution interface rather than insertion of surfactant molecules into the membrane. This hypothesis was supported by a lack of increase in the fluorescence yield of chlorophyll at sub-solubilizing surfactant concentrations, indicating that interactions between the photosynthetic pigment-protein complexes are not extensively disrupted. Difference spectroscopy revealed that long-wavelength (greater than 690 nm) chlorophyll molecules are perturbed by the surfactant. We conclude that at sub-solubilizing concentrations, surfactants specifically interact with exposed Photosystem I components on the surface of the thylakoid membrane. It appears that use of sub-solubilizing concentrations of surfactants has the potential to provide much useful information about the structure and organization of the thylakoid membrane.