Vibrational Raman and infrared spectroscopy are used to probe the dynamical, conformational, functional and thermodynamic properties of both model and intact membrane assemblies. Emphasis is placed on elucidating both lipid-lipid and lipid-protein interactions within the bilayer aggregate. For example, the association between ferricytochrome c and hydrated zwitterionic phospholipid bilayers comprised of dipalmitoylphosphatidycholine (DPPC) were studied using Raman spectroscopic techniques. The protein-lipid reconstituted liposomes were examined under varying conditions of protein concentrations, PH and ionic strength; spectra were reported as a function of temperature. The two most important spectral scattering parameters used to monitor bilayer order/disorder characteristics were total, integrated band intensities and relative peak height intensities. These quantities, which reflected a variety of intramolecular and intermolecular processes, are invariant to changes in PH and ionic strength, but were sensitive to protein concentration. Ferricytochrome c and DPPC form non-stoichiometric complexes capable of altering bilayer packing properties and the temperature behavior of the liposomal assemblies. For the extrinsic ferricytochrome c protein, concentrations of approximately 10- 4M to <10- 5M result in bilayer penetrations which lead to significant membrane perturbations. A new technique, Fourier-transform Raman spectroscopy using near infrared Nd:YAG laser excitation, was developed for determing Raman spectra of highly fluorescing biological samples. (Raman spectra of flourescing systems cannot be obtained when conventional, visible laser techniques are used with dispersive sytems.)
Showing the most recent 10 out of 16 publications
