STRUCTURAL FEATURES UNDERLYING THE ANESTHETIC-INDUCED EQUILIBRIUM BETWEEN 3 SPECTRAL SPECIES OF BACTERIORHODOPSIN - BR(570), BR(480) AND BR(380)

In the presence of halogenated anesthetics and under moderate pH conditions, bacteriorhodopsin exists in equilibrium between three different spectral forms absorbing at 570, 480 and 380 nm. We examined the pigment containing these three chromophores by means of resonance Raman and FT-IR spectroscopy. Our results show that in the 480 nm chromophore the protonation state of the retinal Schiff base is not different from that of the native 570 nm bacteriorhodopsin. The FT-IR spectra indicate that the sequential formation of bR480 and bR380 is accompanied by a reversible disorientation of the pigment alpha helices with respect to one another, and that the phenomenon remains fully reversible as long as the secondary structure of the helices is not modified.