High molecular weight serine protease inhibitors (serpins) are large superfamily of proteins, which bind to and inactivate serine proteinases. In 1995 Sprecher et al. cloned 2 novel serpins, termed PI8 and PI9, from human placenta cDNA library. Sequencing showed that PI8 encodes 376-amino acids. PI8 are localized to the cytoplasm of transfected cells and was able to form an SDS- complex. PI8 is implicated to inhibit furin enzymatic activity and plays a role in platelet-regulated pathophysiological responses.
