Evidence for the existence of an unfolding intermediate state for aminoacylase during denaturation in guanidine solutions

Ji Hong Bai, Dong Xu, Hong Rui Wang, Si Yang Zheng, Hai Meng Zhou

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The equilibrium unfolding of pig kidney aminoacylase in guanidinium chloride (GdmCl) solutions was studied by following the fluorescence and circular dichroism (CD). At low concentrations of GdmCl, less than 1.0 M, the fluorescence intensity decreased with a slight red shift of the emission maximum (from 335 to 340 nm). An unfolding intermediate was observed in low concentrations of denaturant (between 1.2 and 1.6 M GdmCl). This intermediate was characterized by a decreased fluorescence emission intensity, a red-shifted emission maximum, and increased binding of the fluorescence probe 1-anilino-8-naphthalenesulfonate. No significant changes of the secondary structure were indicated by CD measurement. This conformation state is similar to a molten globule state which may exist in the pathway of protein folding. Further changes in the fluorescence properties occurred at higher concentrations of GdmCl, more than 1.6 M, with a decrease in emission intensity and a significant red shift of the emission maximum from 340 to 354 nm. In this stage, the secondary structure was completely broken. A study of apo-enzyme (Zn2+-free enzyme) produced similar results. However, comparison of the changes of the fluorescence emission spectra of native (Holo-) enzyme with Zn2+-free (Apo-) enzyme at low GdmCl concentrations showed that the structure of the Holo-enzyme was more stable than that of the Apo-enzyme. Copyright (C) 1999 Elsevier Science B.V.

Original languageEnglish (US)
Pages (from-to)39-45
Number of pages7
JournalBiochimica et Biophysica Acta - Protein Structure and Molecular Enzymology
Issue number1
StatePublished - Feb 10 1999

All Science Journal Classification (ASJC) codes

  • Biophysics
  • Structural Biology
  • Biochemistry
  • Molecular Biology


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