Human cathepsin B is a metastable enzyme stabilized by specific ionic interactions associated with the active site.
The effect of neutral or alkaline pH on cathepsin B activity and structure was investigated. An irreversible loss of activity, accompanied by large structural changes, was observed at pH > or = 7.0. The high activation energy of 183.5 kJ mol-1, calculated for the inactivation process, is in good agreement with structural changes observed by circular dichroism. Both the pH-induced inactivation and the pH-induced unfolding of cathepsin B were found to be first-order processes, exponentially increasing with increasing pH of the solution. The good agreement of the rate constants of inactivation and unfolding of the enzyme indicates an important structure-function relationship. Cathepsin B was also found to be destabilized both by increasing ionic strength and organic solvent content.
Turk
B
B
Department of Biochemistry and Molecular Biology, J. Stefan Institute, Ljubljana, Slovenia.
Dolenc
I
I
Zerovnik
E
E
Turk
D
D
Gubensek
F
F
Turk
V
V
D001665:Binding Sites; D002401:Cathepsin B / Q000737:chemistry*; D002942:Circular Dichroism; D004795:Enzyme Stability; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008956:Models, Chemical; D008958:Models, Molecular; D009994:Osmolar Concentration; D011487:Protein Conformation; D013154:Spleen / Q000201:enzymology; D013696:Temperature
D002401:Cathepsin B