Spin Label Study of Water Binding and Protein Mobility in Lysozyme

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To better understand, at the molecular level, protein behavior in reduced-water environments, lysozyme was labeled with TEMPO-todoacetamide (TEMPO-IA), a small amphiphilic nitroxide spin label, and equilibrated over phosphorus pentoxide or saturated salt solutions to & Ml range (0-1.0) of water activities. Changes in solvent environment detected by die spin label at 0.11, 0.32, and 0,75 parallel the sigmoida! moisture sorption isotherm transitions. Changes in TEMPO spectra vs protein hydration support water binding in clusters at discrete locations rather than in uniform layers on the protein surface. Motion of the TEMPO-IA was very slow (t -108 sec) and increased progressively with hydration as predicted by the glass transition theory. Paradoxically, the order parameter increased with hydration. Apparently, with hydration dry protein, which had been fixed in random orientation, became more mobile and able to associate and align, thus increasing the order and orientation of the spin label. Overall, results support both sorption isotherm and glass transition models of hydration and molecular motion, and demonstrates unique promise for use of spin labels to obtain information about hydration localization and effects on solvent environment and molecular mobility in food systems.

Original languageEnglish (US)
Pages (from-to)98-113
Number of pages16
JournalACS Symposium Series
StatePublished - 2002

All Science Journal Classification (ASJC) codes

  • General Chemistry
  • General Chemical Engineering


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