Identification of neutral proteases in human neutrophil granules that degrade articular cartilage proteoglycan

Abstract

Human polymorphonuclear neutrophil (PMN) granule extract (25 m̈g of protein) released 60% of the available ³⁵SO₄ from labeled rabbit articular cartilage in 0.5 hour at neutral pH. N‐acetyl‐L‐alanyl‐L‐alanyl‐L‐prolyl‐L‐alanine chloromethyl ketone (NAc‐AAPACK), a specific elastase inhibitor, was only minimally effective against whole granule extract, and N‐α‐tosyl‐L‐lysine chloromethyl ketone, which inhibits trypsin but not elastase, was completely ineffective. Preparative disc‐gel electrophoresis of PMN granule extract revealed two separate regions with independent activity against ³⁵SO₄‐labeled cartilage. One region contained elastases and, when tested alone, was completely inhibited by NAcAAPACK. The other contained lysozyme and two esterases active against N‐acetyl‐L‐phenylalanine‐α‐naphthol. Purified lysozyme proved inactive, suggesting that the chymotrypsin‐like esterases were responsible for proteoglycan degradation by this region of the gel.