1. Cathepsin B-like activity was measured in lung secretions by using the fluorimetric substrate benzyloxycarbonyl-l-arginine-l-arginine-4-methyl-7-coumarylamide (Z-Arg-Arg-MEC). The enzyme had a pH optimum of approximately 5.5 and had the characteristics of an alkaline-stable cysteine proteinase.
2. Enzyme activity in the sputum from ten subjects with chronic bronchitis was significantly reduced after 5 days’ treatment with prednisolone.
3. Seven patients with bronchiectasis were studied before and after 14 days’ treatment with amoxycillin. Cysteine proteinase activity was significantly reduced after 7 days’ therapy, in parallel with a change in sputum quality from purulent to mucoid. One week after cessation of treatment enzyme levels were again increased but were still significantly lower than pretreatment values.
4. Enzyme activity in 21 bronchoalveolar lavage specimens correlated significantly with neutrophil counts but not with macrophage counts.
5. Cysteine proteinase activity in lung secretions resembles that of cathepsin B but is alkaline-stable, suggesting it is a distinct enzyme. The levels of cysteine proteinase in lung secretions appear to be related to the presence of inflammation or infection.