<> "The repository administrator has not yet configured an RDF license."^^ . <> . . . "α-Helix peptide folding and unfolding activation barriers: A nanosecond UV resonance raman study"^^ . "We used UV resonance Raman spectroscopy to characterize the equilibrium conformation and the kinetics of thermal denaturation of a 21 amino acid, mainly alanine, α-helical peptide (AP). The 204-nm UV resonance Raman spectra show selective enhancements of the amide vibrations, whose intensities and frequencies strongly depend on the peptide secondary structure. These AP Raman spectra were accurately modeled by a linear combination of the temperature-dependent Raman spectra of the pure random coil and the pure α-helix conformations; this demonstrates that the AP helix-coil equilibrium is well-described by a two-state model. We constructed a new transient UV resonance Raman spectrometer and developed the necessary methodologies to measure the nanosecond relaxation of AP following a 3-ns T- jump. We obtained the T-jump by using a 1.9-μm IR pulse that heats the solvent water. We probed the AP relaxation using delayed 204-nm excitation pulses which excite the Raman spectra of the amide backbone vibrations. We observe little AP structural changes within the first 40 ns, after which the α-helix starts unfolding. We determined the temperature dependence of the folding and unfolding rates and found that the unfolding rate constants show Arrheniustype behavior with an apparent κ8 kcal/mol activation barrier and a reciprocal rate constant of 240 ± 60 ns at 37 °C. However, the folding rate constants show a negative activation barrier, indicating a failure of transitionstate theory in the simple two-state modeling of AP thermal unfolding, which assumes a temperature-independent potential energy profile along the reaction coordinate. Our measurements of the initial steps in the α-helical structure evolution support recent protein folding landscape and funnel theories; our temperature-dependent rate constants sense the energy landscape complexity at the earliest stages of folding and unfolding."^^ . "1999-09-08" . . "121" . "35" . . "Journal of the American Chemical Society"^^ . . . "00027863" . . . . . . . . . . . . . . . . "SA"^^ . "Asher"^^ . "SA Asher"^^ . . "IK"^^ . "Lednev"^^ . "IK Lednev"^^ . . "MC"^^ . "Sparrow"^^ . "MC Sparrow"^^ . . "AS"^^ . "Karnoup"^^ . "AS Karnoup"^^ . . . . . . "α-Helix peptide folding and unfolding activation barriers: A nanosecond UV resonance raman study (Plain Text)"^^ . . . "licence.txt"^^ . . . "α-Helix peptide folding and unfolding activation barriers: A nanosecond UV resonance raman study (Other)"^^ . . . . . . "indexcodes.txt"^^ . . "HTML Summary of #17791 \n\nα-Helix peptide folding and unfolding activation barriers: A nanosecond UV resonance raman study\n\n" . "text/html" . .