Serpin A1 is also known as Alpha-1-antitrypsin (A1AT), serum trypsin inhibitor, alpha-1 proteinase inhibitor (A1PI), AAT, which belongs to the serpin family. Most serpins inactivate enzymes by binding to them covalently, requiring very high levels to perform their function. Like all serine protease inhibitors, A1AT has a characteristic secondary structure of beta sheets and alpha helices. Serpin A1 / A1AT is inhibitor of serine proteases. Its primary target is elastase, but it also has a moderate affinity for plasmin and thrombin. Irreversibly inhibits trypsin, chymotrypsin and plasminogen activator. The aberrant form of SerpinA1 inhibits insulin-induced NO synthesis in platelets, decreases coagulation time and has proteolytic activity against insulin and plasmin. Serpin A1 / A1AT protects tissues from enzymes of inflammatory cells, especially neutrophil elastase. Defects in SERPINA1 are the cause of alpha-1-antitrypsin deficiency (A1ATD).