Alpha 1 Antitrypsin, also known as SERPINA1, is a plasma protein synthesised in the liver. It consists of a single polypeptide chain and has a molecular weight of 52 kDa. A serine protease inhibitor, its primary function is the protection of lung tissue from the action of neutrophil elastase. The average level of alpha 1 Antitrypsin in plasma is 1.3 g/l.