Human-polymorphonuclear-leucocyte neutral protease and its inhibitor. Studies with fluorescein-labelled polymeric collagen fibrils as a substrate.

Human polymorphonuclear leucocytes were obtained from the synovial fluids of patients with inflamed knee joints suffering either from Reiter's syndrome or from rheumatoid arthritis. The polymorphonuclear leucocytes were collected by gentle centrifugation followed by disruption and their subcellular fractionation by centrifugation in 0.34 M sucrose to provide a granule fraction and a post-granule supernatant fraction. 0.5 M KCl extraction of the granule fraction yielded neutral protease activity, similar to trypsin, when assayed against fluorescein-labelled polymeric collagen fibrils. The post-granule supernatant fraction contained an inhibitor towards the neutral protease and trypsin. The inhibition of the neutral protease was found to be time-dependent, this inhibition being released after 1.5-2 h. In contrast, the inhibition of trypsin was irreversible and this property was used to devise an assay procedure for the inhibitor.