title: Characterization of a stable intermediate in the unfolding of diazoacetylglycine ethyl ester--pepsin by urea.
abstract: The irreversible unfolding of covalently inhibited swine pepsin by urea was studied by spectrophotometric and viscosity measurements. At pH 4.5 and 25 degrees C in 8 M urea, a stable intermediate form of the protein was detected. It differed from the native protein by a slight loss of secondary structure and an increased intrinsic viscosity ([pi] = 7.5 mL g-1), indicating the intermediate to have an increased molecular volume or to be more asymmetric in shape. The protein was transformed into a random coil form by increases of temperature and pH. Comparison with other results suggested that at pH 6 pepsin is less stable than its inactive precursor, pepsinogen, by about 3 Kcal mol-1 (1 cal = 4.187 J).
mesh_terms: D001391:Azo Compounds / Q000031:analogs & derivatives; D002942:Circular Dichroism; D005998:Glycine / Q000031:analogs & derivatives; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D010434:Pepsin A / Q000031:analogs & derivatives*; D010435:Pepsinogens; D011487:Protein Conformation / Q000187:drug effects; D011489:Protein Denaturation; D014508:Urea / Q000494:pharmacology*
chemical_list: D001391:Azo Compounds; D010435:Pepsinogens; C024628:diazoacetylglycine ethyl ester-pepsin; D014508:Urea; D010434:Pepsin A; D005998:Glycine