Transient UV Raman spectroscopy finds no crossing barrier between the peptide alpha-helix and fully random coil conformation.
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.
Lednev
I K
IK
Contribution from the Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA.
Karnoup
A S
AS
Sparrow
M C
MC
Asher
S A
SA
D007700:Kinetics; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D013059:Spectrum Analysis, Raman; D013816:Thermodynamics