Delipidation of Purple Membrane for Size-Tunable Bacteriorhodopsin Biomaterials

Report No. ARL-TR-5938
Authors: Margo E. Goodall, Nabila Hoque, Mark H. Griep, Tammy Hart, and Shashi P. Karna
Date/Pages: February 2012; 18 pages
Abstract: Bacteriorhodopsin (bR), a protein found exclusively in the purple membrane (PM) of the bacteria Halobacterium salinarum, functions as an efficient and robust light-activated proton pump. Its light-harvesting properties are due to a retinal chromophore that changes conformation upon exposure to photons. For use in a titanium oxide (TiO2) bio-sensitized solar cell, the PM fragments containing bR can be made smaller to fit within the TiO2 nanotube pores. The goal of this research is to reduce the PM size surrounding the protein using detergent-mediated solubilization of lipids. To achieve the goal, octyl-b-d-glucopyranoside was used to delipidate the membrane to a point of (1) maximal lipid solubilization and (2) minimal denaturation by keeping the absorbance peaks of 280/570 nm as close to a two-to-one ratio as possible. Micro-volume ultraviolet (UV)-visible (Vis) was used to determine the absorbance spectrum of bR, which was documented for changes throughout the delipidation process. As the PM fragments were solubilized, the ratio of the 280/570-nm absorbance peaks grew from the original ratio of two. After centrifugation to remove the larger PM fragments, the delipidated PM fragment size was determined by ion exclusion spectroscopy and dynamic light scattering.
Distribution: Approved for public release
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Last Update / Reviewed: February 1, 2012