title: Librational fluctuations in protein glasses.
abstract: Librational motions in the region of the protein "glass" (or dynamic) transition are analysed for spin-labelled haemoglobin, serum albumin and β-lactoglobulin by EPR spectroscopy. A discontinuity in the temperature dependence of the mean-square librational amplitude, <α(2)>, occurs in the region of 200K as found for the mean-square atomic displacement, <r(2)>, at the protein dynamic transition by Mössbauer spectroscopy and neutron scattering. The discontinuity in <α(2)> vs. T can be described by the Vogel-Tammann-Fulcher equation, implying a finite glass transition temperature. Above the dynamic transition, <α(2)> vs. 1/T can be approximated by the Arrhenius law with activation energies similar to those usually found for <r(2)>, and relaxation processes in glass-forming media and the hydration shells of proteins. Similar results are found for librational fluctuations of membranous Na,K-ATPase spin-labelled either on superficial SH groups or on those essential to activity.
authors.affiliation: Max-Planck-Institut für biophysikalische Chemie, Göttingen, Germany. dmarsh@gwdg.de
authors.forename: Derek
authors.initials: D
authors.lastname: Marsh
authors.forename: Rosa
authors.initials: R
authors.lastname: Bartucci
authors.forename: Rita
authors.initials: R
authors.lastname: Guzzi
authors.forename: Luigi
authors.initials: L
authors.lastname: Sportelli
authors.forename: Mikael
authors.initials: M
authors.lastname: Esmann
mesh_terms: D000818:Animals; D002417:Cattle; D004578:Electron Spin Resonance Spectroscopy; D005898:Glass / Q000737:chemistry*; D006454:Hemoglobins / Q000737:chemistry*; D006801:Humans; D007782:Lactoglobulins / Q000737:chemistry*; D011506:Proteins / Q000737:chemistry*; D012709:Serum Albumin / Q000737:chemistry*; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry*; D013113:Spin Labels
chemical_list: D006454:Hemoglobins; D007782:Lactoglobulins; D011506:Proteins; D012709:Serum Albumin; D013113:Spin Labels; D000254:Sodium-Potassium-Exchanging ATPase