Time Resolved and Ultraviolet Resonance Raman Spectroscopy of Biological Molecules

The advent of reliable high-power pulsed lasers has enabled the development of Raman spectroscopy in two important directions: a) time-resolved studies of transient species and b) resonance enhancement with ultraviolet excitation. The four convenient wavelengths produced by the YAG laser fourth harmonic (266 nm) and the first, second, and third antiStokes H 2 -shifted lines (240, 218, and 200 nm) are narticular-ly useful for probing a variety of UV chromophores that occur widely in biology. Good quality spectra have been obtained at these wavelengths for proteins, and also for the constituent peptide, phenylalanine, tyrosine, and tryptophan chromophores, and for nucleic acids and the nucleotides. Time-resolved studies have focussed on transient states of hemoglobin (Hb), following the photolysis of the CO complex, in order to elucidate the protein dynamics of this important molecule. Using visible and ultraviolet excitation, it is possible to monitor both the heme groups and the aromatic residues in the protein. The UVRR spectra indicate that a T-like quaternary structure is formed within 7 ns of HbCO photolysis, implying a surprisingly rigid connection between the heme groups and the subunit interfaces.