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A simple method for determination of rotational correlation times and separation of rotational and polarity effects from EPR spectra of spin-labeled biomolecules in a wide correlation time range.

Authors
  • Steinhoff, H J1
  • 1 Institut für Biophysik, Ruhr-Universität Bochum, F.R.G.
Type
Published Article
Journal
Journal of Biochemical and Biophysical Methods
Publisher
Elsevier
Publication Date
Dec 01, 1988
Volume
17
Issue
4
Pages
237–247
Identifiers
PMID: 2854146
Source
Medline
License
Unknown

Abstract

A method using nitroxide radical spin labels for determining both the isotropic rotational correlation time tau R and the environmental polarity of the label is described. By means of a least square fitting method, the values of an effective hyperfine tensor A' and of an effective g value tensor g' of randomly oriented spin labels are determined from X-band EPR spectra on the basis of an effective time-independent Hamiltonian. The traces of the tensors deliver the information about the environmental polarity of the label and are not dependent on the rotational correlation time tau R. A new averaging parameter S (tau R), calculated on the basis of the principal values of the tensor A', permits the evaluation of the rotational correlation time tau R in a very wide time range between 10(-10) and 10(-6) s. An application of this method to spin-labeled methemoglobin over a large temperature range and in environments of different polarity is discussed.

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