Spectral broadening of the Soret band in myoglobin: an interpretation by the full spectrum of low-frequency modes from a normal modes analysis.
In this work the temperature dependence of the Soret band line shape in carbon-monoxy myoglobin is re-analyzed by using both the full correlator approach in the time domain and the frequency domain approach. The new analyses exploit the full density of vibrational states of carbon-monoxy myoglobin available from normal modes analysis, and avoid the artificial division of the entire set of vibrational modes coupled to the Soret transition into "high-frequency" and "low-frequency" subsets; the frequency domain analysis, however, makes use of the so-called short-times approximation, while the time domain one avoids it. Time domain and frequency domain analyses give very similar results, thus supporting the applicability of the short-times approximation to the analysis of hemeprotein spectra; in particular, they clearly indicate the presence of spectral heterogeneity in the Soret band of carbon-monoxy myoglobin. The analyses also show that a temperature dependence of the Gaussian width parameter steeper than the hyperbolic cotangent law predicted by the Einstein harmonic oscillator and/or a temperature dependence of inhomogeneous broadening are not sufficient to obtain quantitative information on the magnitude of an-harmonic contributions to the iron-heme plane motion. However, the dependence of the previous two quantities may be used to obtain semiquantitative information on the overall coupling of the Soret transition to the low-frequency modes and therefore on the dynamic properties of the heme pocket in different states of the protein.
Cupane
Antonio
A
Istituto Nazionale per la Fisica della Materia (INFM), Dipartimento di Scienze Fisiche e Astronomiche dell'Università, Via Archirafi 36, 90123 Palermo, Italy. cupane@fisica.unipa.it
Cammarata
Marco
M
Cordone
Lorenzo
L
Leone
Maurizio
M
Vitrano
Eugenio
E
Engler
Niklas
N
Parak
Fritz
F
D003198:Computer Simulation; D008956:Models, Chemical; D009211:Myoglobin / Q000032:analysis* / Q000737:chemistry*; D013057:Spectrum Analysis / Q000379:methods*; D013696:Temperature; D014732:Vibration
D009211:Myoglobin