PICOSECOND TR3 SPECTROSCOPY OF BACTERIORHODOPSIN

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The research program is intended to elucidate the molecular dynamics associated with bacteriorhodopsin (BR) as it relates to its function as a proton and ion pump in biochemical membranes and to its role as a structural and conformational model for visual pigments. Time-resolved resonance Raman (TR3) spectroscopy is the experimental technique of primary interest since it can be used to provide structural, conformational, and kinetic information simultaneously. Many of the measurements proposed here are now feasible because of the recent development of a versatile picosecond TR3 (PTR3) spectrometer. One important consequence of these expanded instrumental capabilities is that PTR3 spectra can be recorded for room temperature samples under wavelength and intensity conditions which emulate those of the normal BR photocycle. Projects to be undertaken include the: (1) recording of PTR3 spectra of intermediates as a function of reaction time with a pump-probe configuration optimized for excitation and probing separately, (2) time-resolved antistokes Raman studies of temperature effects arising from rapid intramolecular heating during optical excitation, (3) examination of the time-dependent protein response to retinal excitation, and (4) measurement of time-resolved excitation profiles of intermediates to study protein environment effects on retinal conformation and protonation and to optimize resonance Raman detection for individual intermediates.