Denaturation behavior of alpha-chymotrypsinogen A in urea and alkylurea solutions: fluorescence studies.
The solvent denaturation of alpha-chymotrypsinogen (alpha-ctg A) in aqueous solution of urea, methyl-, N,N'-dimethyl-, ethyl-, propyl- and butylurea was studied by fluorescence measurements. Data were analyzed on the assumption of a two-state approximation to obtain the apparent equilibrium constant, Ku and the apparent Gibbs free energy of transition delta G0u. It has been observed that alkyl-substitution of urea significantly lowers the denaturant concentration needed to denature alpha-ctg A at 25 degrees C. Denaturation was accompanied by the red shift of emission maxima, the increase of the half-width of the fluorescence spectra, the increase of the fluorescence intensity, and the decrease of the fluorescence polarization. The differences of these fluorescence parameters observed for alpha-ctg A in alkylureas and urea can be ascribed to different unfolded states of the protein in different denaturant solutions. Minor differences in the extent of unfolding were confirmed by size-exclusion chromatography.
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Department of Chemistry, University of Ljubljana, Slovenia.
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D000818:Animals; D002417:Cattle; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002845:Chromatography / Q000379:methods; D002919:Chymotrypsinogen / Q000737:chemistry*; D004355:Drug Stability; D005454:Fluorescence Polarization; D005470:Fluorometry; D006863:Hydrogen-Ion Concentration; D008782:Methylurea Compounds / Q000737:chemistry*; D011489:Protein Denaturation; D017510:Protein Folding; D011498:Protein Precursors / Q000737:chemistry*; D012996:Solutions; D013050:Spectrometry, Fluorescence; D014364:Tryptophan / Q000032:analysis; D014508:Urea / Q000031:analogs & derivatives / Q000737:chemistry*; D014867:Water
D008782:Methylurea Compounds; D011498:Protein Precursors; D012996:Solutions; D014867:Water; D014364:Tryptophan; D014508:Urea; D002919:Chymotrypsinogen; C018275:1,1-dimethylurea; C002352:methylurea