title: A circular dichroism study on thermal denaturation of a dimeric globular protein, Streptomyces subtilisin inhibitor.
abstract: Thermal denaturation of Streptomyces subtilisin inhibitor was studied by means of circular dichroism (CD) measurements in the far-UV and near-UV regions. The denaturation was found to be largely reversible; the partial irreversibility was associated with a slight loss of the inhibitory activity. Difference CD spectra in the far-UV region clarified the existence of two distinct steps in the thermal transition of the secondary structure. The first step below 80 degrees C is attributable to a partial conformational change in the alpha-helix portion, whereas the second step between 80 degrees C and 94 degrees C is attributable to a major conformational change involving the beta-sheet portion. On the assumption that the major denaturation involves dissociation of the SSI into its subunits, the enthalpy and entropy changes were determined to be 216 kcal X mol-1 and to be 603 cal X deg-1 X mol-1, respectively.
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D002942:Circular Dichroism; D007700:Kinetics; D046911:Macromolecular Substances; D011487:Protein Conformation; D011489:Protein Denaturation; D013056:Spectrophotometry, Ultraviolet; D013381:Subtilisins / Q000037:antagonists & inhibitors*; D013816:Thermodynamics
chemical_list: D001426:Bacterial Proteins; D046911:Macromolecular Substances; C018150:subtilisin inhibitor protein, Streptomyces; D013381:Subtilisins