Monovalent Cations Depress the Unfolding of the α-Helical Bacteriorhodopsin at the Air-Water Interface

概要

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The structural changes of bacteriorhodopsin (bR) in purple membrane (PM) at the air-water interface and the effects of monovalent cations were examined using a monolayer technique and Fourier transform IR spectroscopy. The low initial coverage (c_i) of the interface with PM films significantly caused the denaturation of bR accompanied by a collapse in the PM bilayer structure. The IR spectra of LB films of the PM monolayer films showed that the α-helical bR molecule in the PM film was partially transformed into a β-sheet depending on the c_i value. The surface pressure-area (π-A) isotherms of the PM films in the presence of 50 mM alkali metal chlorides were condensed in the sequence Cs^+>K^+>Na^+>Li^+. The α-helix content of bR in the PM films in the presence of 50 mM alkali metal chloride was 84.3% for Cs^+, 83.5% for K^+, 78.9% for Na^+, and 76.0% for Li^+, comparable to 68.2%, the value for the subphase ion-free water. The present data indicated that the unfolding of the α-helical bR in the PM monolayer films was depressed by the addition of small amounts of monovalent cations into the subphase water.
公益社団法人日本薬学会の論文
1995-01-15