EFFECT OF AN INTERSUBUNIT DISULFIDE BOND ON THE STABILITY OF STREPTOMYCES SUBTILISIN INHIBITOR

The effect of an engineered disulfide bond between two identical subun its of a dimeric protein, Streptomyces subtilisin inhibitor, on the st ability of the protein was studied by differential scanning calorimetr y. The introduction of the linkage caused a large stabilization withou t changing the cooperativity of unfolding, with the denaturation tempe rature of a 2 mg/mL solution being increased by 14.3 degrees C to 95.0 degrees C at pH 9.5 and by 16.4 degrees C to 63.0 degrees C at pH 3.0 . The stabilization was caused by a loss of denaturational entropy, i. e., -40 and -98 cal K-1 mol(-1) at pH 3.0 and 9.5, respectively, which more than compensated for the loss in the denaturational enthalpy.