FTIR spectroscopic study of the dynamics of conformational substates in hydrated carbonyl-myoglobin films via temperature dependence of the CO stretching band parameters
1994; Elsevier BV; Volume: 67; Issue: 2 Linguagem: Inglês
10.1016/s0006-3495(94)80547-8
ISSN1542-0086
Autores Tópico(s)Protein Structure and Dynamics
ResumoTwo hydrated carbonyl myoglobin (MbCO) films, one containing (0.30 g water)/(g MbCO) from MbCO solution in water at pH 5.5 and te other (0.32 g water)/(g MbCO) from 0.1 M potassium phosphate buffer solution at pH 6.8, were studied by FTIR spectroscopy from 293 K to 78 K at selected temperatures on cooling and reheating.Above -180 K the general trend in temperature dependence of half-bandwidths, peak naxima, and band area ratios of the Al and A3 conformer bandls is similar to those reported by Ansari et al. (1987.Biophys.J. 26:337) for MbCO in 75% glycerol/water solution, but abrupt changes in sbpes at -1 80-200 K and freezing-in of conformer populations, which could be taken as indicator for glass btansition of the solvent or the protein, are absent for the hydrated MbCO films.This is interpreted in terms of an exceptonally broad distribution of relaxation times, and is in accord with conclusions from recent calorimetric annealing studies of hydrated protein powders (Sartor et al. 1994.Biophys.J. 66:249).Exchange between the three A conformers does not stop at -1 80-200 K but occurs over the whole temperature region studied.These results are Fen diussed with respect to MbCO's behavior in the glass-* liquid trnsibon region of glass-forming solvents, and it is concluded that, in analogy to the behavior of low-molecular-weight com- pounds with a distribution of rapidly interconverting conformners, freezing-in of MbCO's A conformer populations by the solvent should not be mistaken for a glass transition of MbCO.
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