BACTERIORHODOPSIN - A MOLECULAR PHOTOSCILLATOR

Using an established fluorescence probe we detected light-induced oscillations in the electrical potential gradient in the membranes of bacteriorhodopsin-containing envelope vesicles of Halobacterium halobium. They resisted treatments which are known to inactivate other ion translocating systems and the H+/ATPase, and were also present in bacteriorhodopsin-containing liposomes. Under specific illumination regimes, bacteriorhodopsin (bR) concentration and pH the photooscillations became sustained and exhibited properties typical of nonlinear oscillators. The liposomes also showed sustained oscillations in the pH of the medium. These observations strongly suggest that bacteriorhodopsin itself manifests the positive feedback elements necessary for these oscillatory phenomena. Because feedback parameters determine amplitudes, frequency and phases of oscillations a new regulatory mechanism of these chromoproteins may have become apparent.