Fluorescence studies of the effect of pH, guanidine hydrochloride and urea on equinatoxin II conformation.
The solvent denaturation of equinatoxin II (EqTxII) in aqueous solutions of urea, guanidine hydrochloride (Gu-HCl) and at various pH values was examined by monitoring changes in the protein intrinsic emission fluorescence spectra and in the fluorescence spectra of the added external probe ANS. It has been observed that EqTxII denaturation is reflected in a strong red shift of intrinsic fluorescence emission maxima accompanied by a simultaneous decrease in fluorescence intensity and that guanidine hydrochloride is significantly more powerful denaturant than urea or changing of pH. Comparison of intrinsic fluorescence spectra of EqTxII denatured by one of the three denaturing agents has shown that the fully denatured states of the protein in Gu-HCl and urea are similar and substantially different from those induced by changing of pH. Furthermore, according to the measurements of the ANS-fluorescence in EqTxII solutions as a function of pH the protein exists at pH values below 2.0 in an acid-denatured compact state.
Malavasic
M
M
Department of Chemistry, University of Ljubljana, Slovenia.
Poklar
N
N
Macek
P
P
Vesnaver
G
G
D000817:Anilino Naphthalenesulfonates; D000818:Animals; D003064:Cnidarian Venoms / Q000737:chemistry*; D003603:Cytotoxins; D005456:Fluorescent Dyes; D019791:Guanidine; D006146:Guanidines / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D011487:Protein Conformation / Q000187:drug effects; D011489:Protein Denaturation; D012615:Sea Anemones; D013050:Spectrometry, Fluorescence; D014508:Urea / Q000494:pharmacology
D000817:Anilino Naphthalenesulfonates; D003064:Cnidarian Venoms; D003603:Cytotoxins; D005456:Fluorescent Dyes; D006146:Guanidines; C012307:equinatoxin; C027132:1-anilino-8-naphthalenesulfonate; D014508:Urea; D019791:Guanidine