Putative serine protease inhibitor. Interacts with CANX AND PDIA3. Expressed in the liver, leukocytes and testis. Also detected in brain, colon, uterus, esophagus, spleen, trachea, kidney and lung. 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 carboxyl group of the serpin reactive site and the serine hydroxyl of the protease. The resulting inactive serpin-protease complex is highly stable (By similarity). Glycosylated. Was originally thought to be the product of a pseudogene (PubMed:9383284). Later shown to be a protein-coding gene (PubMed:23826168). Seems to be a polymorphic pseudogene which is protein-coding in some individuals and non-coding in others. The sequence shown is that of the V2 allele. Other alleles are: V1 and V3. Belongs to the serpin family.