S. Prajapati et al., ALKALINE UNFOLDING AND SALT-INDUCED FOLDING OF BOVINE LIVER CATALASE AT HIGH PH, European journal of biochemistry, 255(1), 1998, pp. 178-184
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.