Alpha-1-antitrypsin 1-3(SERPIN A1) is a secreted protein and belongs to the serpin family. Serpins bind the protease active site resulting in a major conformational rearrangement that traps the enzyme in a covalent acyl-enzyme intermediate. Mouse SERPIN A1 is a serine protease inhibitor whose targets include elastase,plasmin, thrombin, trypsin, chymotrypsin, and plasminogen activator. Defects in this gene can cause emphysema orliver disease. Several transcript variants encoding the same protein have been found for this gene.