1. The Interdependence of Substrate and Protein Transformations in Rhodanese Catalysis
- Author
-
Shu-Fang Wang and Marguerite Volini
- Subjects
Conformational change ,Circular dichroism ,Stereochemistry ,Cyanide ,Inorganic chemistry ,chemistry.chemical_element ,Rhodanese ,Biochemistry ,Catalysis ,Ion ,chemistry.chemical_compound ,Sulfite ,Polymer chemistry ,Conformational isomerism ,Optical rotatory dispersion ,Molecular Biology ,Equilibrium constant ,chemistry.chemical_classification ,Thiosulfate ,Thiocyanate ,Substrate (chemistry) ,Cell Biology ,Sulfur ,Enzyme ,Catalytic cycle ,chemistry ,Thiosulfate sulfurtransferase - Abstract
The cationic site of the enzyme rhodanese forms ion pairs with the substrate and product anions, thiosulfate, cyanide, sulfite, and thiocyanate. It also forms ion pairs with such diverse anionic species as acetate, formate, sulfate, and glycinate. In rate studies, the equilibrium constants and their temperature dependencies were evaluated for the interactions of most of these anions with both the free enzyme and the sulfur-substituted enzyme intermediate. The ionic strength dependencies of the constants for the substrate, thiosulfate ion, and the inhibitor, sulfate ion, were also determined. The results of this study provide a basis for calculating the relative concentrations of all enzymic species under a broad variety of experimental conditions. Further, the study of the thermodynamic parameters indicates that the enzyme-anion interactions take place in an hydrophobic environment in which ion solvation is minimal. When the parameters of substrate and product origin are compared with those for the other enzyme-anion interactions, the results suggest that the protein undergoes conformational changes during the reaction. The direction of the entropy differences indicates that there are successive changes to a more constrained state on binding of the substrate, thiosulfate ion, and release of the product, sulfite ion, followed by a relaxation of the protein upon release of the product, thiocyanate ion.
- Published
- 1973