Leukocyte elastase is one of several hydrolytic enzymes contained in the azurophil granules of human neutrophils exhibiting a relative molecular weight of 29.5 kDa. The enzyme differs from pancreatic elastase in specificity on synthetic substrates and in inhibitor sensitivity. Leukozyte elastase shows only moderate sequence homology with pancreatic elastase. It has a very narrow specificity, cleaving Val-X bonds preferentially, and Ala-X links to a lesser extent. It has been shown to degrade elastin, cartilage proteoglycans, several collagens and fibronectin. Physiologically, it is involved in the degradation of foreign materials ingested during phagocytosis. Damage to connective tissue caused by leakage of enzymes is normally limited by proteinase inhibitors. It has been suggested that insufficient levels of these inhibitors leads to pulmonary emphysema, and elastase in particular has been implicated in abnormal lung connective tissue turnover.