ALKALINE UNFOLDING AND SALT-INDUCED FOLDING OF BOVINE LIVER CATALASE AT HIGH PH

We have studied the alkaline unfolding of bovine liver catalase and it s dependence on ionic strength by enzymic activity measurements and a combination of optical methods like circular dichroism, fluorescence a nd absorption spectroscopies. Under conditions of high pH (11.5) and l ow ionic strength, the native tetrameric enzyme dissociates into monom ers with complete loss of enzymic activity and a significant loss of c c-helical content. Increase in ionic strength by addition of salts lik e potassium chloride and sodium sulphate resulted in folding of alkali ne-unfolded enzyme by association of monomers to tetramer but with sig nificantly different structural properties compared to native enzyme. The salt-induced tetrameric intermediate is characterized by a signifi cant exposure of the buried hydrophobic clusters and significantly red uced a-helical content compared to the native enzyme. The refolding/re constitution studies showed that the salt-induced partially folded tet rameric intermediate shows significantly higher efficiency of refoldin g/reconstitution as compared to alkaline-denatured catalase in the abs ence of salts. These studies suggest that folding of multimeric enzyme s proceeds probably through the hydrophobic collapse of partially fold ed multimeric intermediate with exposed hydrophobic clusters.