Kinetics of the pH-induced inactivation of human cathepsin L

The kinetics of inactivation of human cathepsin L was studied. The inactivation rate was determined as a function of pH and temperature and compared with the rate constant of cystatin-induced enzyme inactivation. Cathepsin L is an unstable lysosomal cysteine proteinase at neutral or alkaline pH. The results indicate that the inactivation is a first-order process and is inversely related to substrate concentration.