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BioMed Research International
Volume 2013 (2013), Article ID 349542, 7 pages
http://dx.doi.org/10.1155/2013/349542
Research Article

Spectroscopic Studies on Unfolding Processes of Apo-Neuroglobin Induced by Guanidine Hydrochloride and Urea

School of Chemistry and Chemical Engineering, Liaocheng University, No. 1, Hunan Road, Liaocheng 252059, China

Received 18 April 2013; Revised 6 July 2013; Accepted 8 July 2013

Academic Editor: Stefano Curcio

Copyright © 2013 Cui Zhang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Neuroglobin (Ngb), a recently discovered globin, is predominantly expressed in the brain, retina, and other nerve tissues of vertebrates. The unfolding processes of apo-neuroglobin (apoNgb) induced by guanidine hydrochloride (GdnHCl) and urea were investigated by spectroscopic methods. In the unfolding processes, apoNgb's tertiary structural transition was monitored by the changes of intrinsic fluorescence emission spectra, and its secondary structural transition was measured by the changes of far-ultraviolet circular dichroism (CD) spectra. In addition, 8-anilino-1-naphthalenesulfonic acid (ANS), a hydrophobic cluster binding dye, was also used to monitor the unfolding process of apoNgb and to explore its intermediates. Results showed that GdnHCl-induced unfolding of apoNgb was via a three-state pathway, that is, Native state → Intermediate state → Unfolded state , during which the intermediate was inferred by an increase in fluorescence intensity and the change of CD value. Gibbs free energy changes are 10.2 kJ·mol−1 for the first unfolding transition and 14.0 kJ·mol−1 for the second transition. However, urea-induced unfolding of apoNgb only underwent a two-state transition: Native state → Partially unfolded state . The result showed that GdnHCl can efficiently affect the conformational states of apoNgb compared with those of urea. The work will benefit to have an understanding of the unfolding mechanism of apoNgb induced by GdnHCl and urea.