Kinetic resonance Raman spectroscopy of carotenoids: A sensitive kinetic monitor of bacteriorhodopsin mediated membrane potential changes

A rapid (14 - 22 μs) light-induced, bacteriorhodopsin mediated membrane potential has been detected using the technique of kinetic resonance Raman spectroscopy and the model system of β-carotene incorporated into reconstituted vesicles containing bacteriorhodopsin. Our data demonstrate that the kinetic resonance Raman spectrum of β-carotene is an extremely sensitive monitor of kinetic alterations in membrane potential with micron spatial resolution in a highly scattering medium. In addition, our Raman results indicate that the potential sensitivity of β-carotene is an excited state property of the molecule, thus making it an electrochromic monitor of membrane potential. We feel the techniques illustrated in this paper have the advantage of being a native probe of kinetic membrane potential changes and will be applicable to a wide variety of biological systems without the perturbing side-effects which often accompany the use of non-biological, potential-sensitive dyes.