FLUORESCENCE STUDIES OF THE EFFECT OF PH, GUANIDINE-HYDROCHLORIDE ANDUREA ON EQUINATOXIN-II CONFORMATION

The solvent denaturation of equinatoxin II (EqTxII) in aqueous solutio ns of urea, guanidine hydrochloride (Gu-HCl) and at various pH values was examined by monitoring changes in the protein intrinsic emission f luorescence spectra and in the fluorescence spectra of the added exter nal probe ANS, It has been observed that EqTxII denaturation is reflec ted in a strong red shift of intrinsic fluorescence emission maxima ac companied by a simultaneous decrease in fluorescence intensity and tha t guanidine hydrochloride is significantly more powerful denaturant th an urea or changing of pH. Comparison of intrinsic fluorescence spectr a 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 valu es below 2.0 in an acid-denatured compact state.