Ultrasonic Measurement of Bacteriorhodopsin in Purple Membrane

Abstract

Ultrasonic properties of bacteriorhodopsin which is a light-driven proton pump in purple membrane were studied in the dark as well as under illumination. A xenon lamp was added as a light source to a previously developed ultrasonic resonator. Bacteriorhodopsin showed no ultrasonic relaxation in the frequency range of a few megahertz. The adiabatic bulk modulus of bacteriorhodopsin estimated from ultrasonic velocity was about 4×1010 dyn/cm2 in the dark. When bacteriorhodopsin was illuminated, the ultrasonic velocity increased significantly in proportion to the intensity of light.