THE PROTON PUMP BACTERIORHODOPSIN AS A RECEPTOR OF COLOR-VISION IN HALOBACTERIUM-SALINARIUM

A system of photoreception in Halobacterium salinarium based on two co mponents, i.e., the light-dependent generator of Delta ($) over bar mu (H)(+), bacteriorhodopsin, and the as yet unidentified Delta ($) over bar mu(H)(+) receptor, was described earlier. It was shown that it fun ctions as a light sensor over a wide range of wavelengths and transmit s the attractant signal to the flagella of the bacteria on an increase in light intensity. We now show that the same system may sense blue l ight as a repellent through the M(412) intermediate of the bacteriorho dopsin photocycle. The reaction is elicited by the transient decrease in the electric potential difference on the bacterial membrane due to the intramembrane proton translocation which accompanies the blue ligh t induced conversion of the M(412) intermediate to the ground state bR (568).