title: Human neutrophil elastase alters human alpha-thrombin function: limited proteolysis near the gamma-cleavage site results in decreased fibrinogen clotting and platelet-stimulatory activity.
abstract: During blood coagulation, polymorphonuclear leukocytes release elastase in amounts that can exceed 100 nmol/L. We therefore studied the interaction between human leukocyte elastase and human alpha-thrombin. Elastase cleaved the thrombin B chain (Ala 150-Asn 151) near the gamma-cleavage site, resulting in two fragments held together by noncovalent interactions. The NH2-terminal fragment (FI), mol wt approximately 18,000, was disulfide-linked to the thrombin A chain. The COOH-terminal fragment (FII), mol wt approximately 13,000, contained the active-site serine and formed a covalent bond with antithrombin III. Heparin accelerated proteolysis of alpha-thrombin by elastase. Proteolyzed alpha-thrombin (T theta) retained full amidolytic activity; however, the concentration of T theta causing 50% maximal platelet aggregation and adenosine triphosphate (ATP) release was 7.9 nmol/L (1.1 nmol/L for alpha-thrombin and 220 nmol/L for gamma-thrombin). Fibrinogen clotting activity of T theta and gamma-thrombin was 32% and 1% that of alpha-thrombin, respectively. Elastase released during the coagulation process may modulate thrombin activity. In addition, elastase-modified thrombin may be a useful probe of the structure and function of the gamma-cleavage region.
mesh_terms: D000595:Amino Acid Sequence; D000990:Antithrombin III / Q000378:metabolism; D001777:Blood Coagulation / Q000187:drug effects*; D005340:Fibrinogen / Q000378:metabolism*; D006801:Humans; D009504:Neutrophils / Q000201:enzymology*; D010196:Pancreatic Elastase / Q000378:metabolism*; D010974:Platelet Aggregation / Q000187:drug effects*; D012694:Serine / Q000378:metabolism; D013917:Thrombin / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D012694:Serine; D000990:Antithrombin III; D005340:Fibrinogen; D010196:Pancreatic Elastase; D013917:Thrombin