Human Cathepsin B Is a Metastable Enzyme Stabilized by Specific Ionic Interactions Associated with the Active Site

• Published in: Biochemistry (Easton) Vol. 33; no. 49; pp. 14800 - 14806
• Main Authors: Turk, Boris, Dolenc, Iztok, Zerovnik, Eva, Turk, Dusan, Gubensek, Franc, Turk, Vito
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 01-12-1994
• Subjects: Binding Sites; Cathepsin B - chemistry; Circular Dichroism; Enzyme Stability; Humans; Hydrogen-Ion Concentration; Kinetics; Models, Chemical; Models, Molecular; Osmolar Concentration; Protein Conformation; Spleen - enzymology; Temperature
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi00253a019

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.