DISSOCIATION-CONSTANTS AND THERMAL-STABILITY OF COMPLEXES OF BACILLUS-INTERMEDIUS RNASE AND THE PROTEIN INHIBITOR OF BACILLUS-AMYLOLIQUEFACIENS RNASE

Binase, the extracellular ribonuclease of Bacillus intermedias, is inh ibited by barstar, the natural protein inhibitor of the homologous RNa se, barnase, of B. intermedius. The dissociation constants of the bina se complexes with barstar and its double Cys(40,82)Ala mutant are abou t 10(-12) M, only 5 to 43 times higher than those of the barnase-barst ar complex. As with barnase, the denaturation temperature of binase is raised dramatically in the complex. Calorimetric studies of the forma tion and stability of the binase-barstar complex show that the binase reaction with barstar is qualitatively similar to that of barnase but some significant quantitative differences are reported.