title: Transient UV Raman spectroscopy finds no crossing barrier between the peptide alpha-helix and fully random coil conformation.
abstract: Transient UV resonance Raman measurements excited within the amide pi --> pi transitions of a 21 unit alpha-helical peptide has for the first time determined a lower bound for the unfolding rate of the last alpha-helical turn to form a fully random coil peptide. A 3 ns T-jump is generated with 1.9 microm laser pulses, which are absorbed by water. Subsequent 3 ns 204 nm UV pulses excite the amide Raman spectra at delay times between 3 ns and 1 ms, to monitor the peptide conformational evolution. We find approximately 180 ns relaxation times which result in a rate constant of >5 x 10(6) s(-1) for unfolding of the last alpha-helical turn. Our data are inconsistent with slow alpha-helix nuclei melting.
authors.affiliation: Contribution from the Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA.
authors.forename: I K
authors.initials: IK
authors.lastname: Lednev
authors.forename: A S
authors.initials: AS
authors.lastname: Karnoup
authors.forename: M C
authors.initials: MC
authors.lastname: Sparrow
authors.forename: S A
authors.initials: SA
authors.lastname: Asher
mesh_terms: D007700:Kinetics; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D013059:Spectrum Analysis, Raman; D013816:Thermodynamics