Does not inhibit elastase or chymotrypsin. No target protease has been identified to date. The reactive center loop (RCL) extends out from the body of the protein and directs binding to the target protease. The protease cleaves the serpin at the reactive site within the RCL, establishing a covalent linkage between the serpin reactive site and the active site of the protease. The resulting inactive serpin-protease complex is highly stable (By similarity). Variability within the reactive center loop (RCL) sequences of Serpina1-related genes may determine target protease specificity. Murine alpha-1-antitrypsin is represented by a cluster of up to 6 individual Serpina1-related genes. The precise complement of Serpina1-related genes present varies according to the strain of the animal. Belongs to the serpin family.