Ultraviolet resonance Raman spectroscopy of biopolymers

Ultraviolet resonance Raman scattering promises to be a useful technique for investigating the structure, refolding, and isotope exchange behavior of proteins and nucleic acids. Protein-nucleic acid interactions may be particularly amenable to this new method. These preliminary results and many others not reported here have demonstrated that these spectra are quite strongly enhanced, are often distinct from those obtained with visible excitation, are very sensitive to isotopic substitution and conformation, and, in many cases, are sensitive to the detailed wavelength used for excitation. This last observation should prove useful in sorting out complex overlapping bands in proteins by providing a check on any proposed assignment in the form of confirmatory intensity changes. Ultraviolet resonance Raman spectroscopy is also clearly a useful technique for probing the geometries of excited electronic states of these species. It is also likely that this method can be useful in sorting out the complex pattern of electronic excited states of biopolymers. This is particularly needed if other well developed optical methods, such as circular dichroism, are to be put on a firm theoretical foundation. The limits of sensitivity of UV Raman scattering have yet to be determined. Considerable improvements in the quality of spectra have resulted over the past year due primarily to changes in the laser hardware, the use of a high throughput monochromator and signal collection and processing methods. The use of multichannel detection will probably permit studies of micromolar concentration protein solutions. Advances in sample handling methods are clearly needed and reliable internal intensity standards at shorter wavelengths would be useful. Clearly, however, laser technology is no longer the limiting factor in such studies. Methods are now available that permit extension of this technique to wavelengths as short as 150 nm.