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 assuming a two-state mechanism, an apparent free energy of unfolding at zero denaturant concentration, Δ G H 2O app, was found to be 4.4 kcal mole at pH 6.0 and 25°C. By microcalorimetry the enthalpy of denaturation of phycocyanin was found to be −230 kcal mole at 25°C. The relatively large negative enthalpy change results from protein unfolding and changes in protein solvation.
Published Version
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