Anesthetic-Bacteriorhodopsin interaction : Alcohol-Induced Biphasic Effects

The purple membrane is an appropriate model system for investigating the effects of anesthetics on the structures and functions of excitable cell membranes. The effects of anesthetically active alcohols (methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol, and 1-hexanol) on the structure of bacteriorhodopsin (bR) in the purple membrane were investigated by circular dichroism (CD) and adsorbance measurements. These alcohols increased the 530-nm ellipticity of bR at low concentrations of the alcohols and decreased it at high concentrations. The addition of alcohol at a low concentration in the purple membrane aqueous suspension tended to favor the more folded-compact conformation of the bR by the enhancement of hydrophobic interaction. Alcohols at high concentrations caused the cooperative denaturation of bR due to the access of alcohol to the retinal chromophore. Our attention is mainly focused on the finding that alcohols at low concentrations induce a more folded conformation of bR.