In vitro evidence that human airway lysozyme is cleaved and inactivated by Pseudomonas aeruginosa elastase and not by human leukocyte elastase.

The in vitro effects of Pseudomonas aeruginosa elastase (P. aeruginosa E) and of human leukocyte elastase on human airway lysozyme (HAL) were investigated. P. aeruginosa E inactivated and cleaved HAL, whereas human leukocyte elastase had no effect. Total inactivation of HAL by P. aeruginosa E was observed after 120 min of incubation at 37 degrees C, for an elastase-to-lysozyme molar ratio of 1:5. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of reaction mixtures containing HAL and P. aeruginosa E in an elastase-to-lysozyme molar ratio of 1:10 showed a progressive disappearance of the HAL band upon increasing the incubation time with P. aeruginosa E. Gel filtration chromatography indicated that HAL was cleaved into at least three peptide fragments. The cleavage of HAL by P. aeruginosa E was accompanied by parallel losses of its bacteriolytic activity and its immunoreactive property.