title: Denaturation of phycocyanin by urea and determination of the enthalpy of denaturation by microcalorimetry.
abstract: Denaturation of the protein phycocyanin in urea solution was investigated by microcalorimetry, ultraviolet and visible spectroscopy, circular dichroism and sedimentation equilibrium. The results consistently demonstrated that in the presence of 7 M urea this protein is completely denatured. By assumings a two-state mechanism, an apparent free energy of unfolding at zero denaturant concentration, (formula: see text) was found to be 4.4 kcal/mole at pH 6.0 and 25 degrees C. By microcalorimetry the enthalpy of denaturation of phycocyanin app was found to be -230 kcal/mole at 25 degrees C. The relatively large negative enthalpy change results from protein unfolding and changes in protein solvation.
mesh_terms: D001665:Binding Sites; D002942:Circular Dichroism; D000458:Cyanobacteria; D008433:Mathematics; D008968:Molecular Conformation; D010798:Phycocyanin; D010860:Pigments, Biological; D011489:Protein Denaturation; D013053:Spectrophotometry; D013056:Spectrophotometry, Ultraviolet; D013816:Thermodynamics; D014508:Urea
chemical_list: D010860:Pigments, Biological; D010798:Phycocyanin; D014508:Urea