Sodium salicylate activates cathepsin B but not cathepsin H from rat spleen.

Effect of sodium salicylate (SA) and its analogues on lysosomal cysteine proteinases, cathepsins B and H, was investigated. Using a sensitive fluorometric assay, SA was shown to activate cathepsin B but not cathepsin H in the presence of cysteine. Kinetics data showed that the SA-stimulated reaction was due to a 4.5-fold decrease in Km. SA caused a decrease in the inactivation rate of cathepsin B by leupeptin and E-64. It was suggested that SA stimulates the activation process of the essential cysteine residue.