<n0:ComplexDefinition xmlns:n0="http://ncicb.nci.nih.gov/xml/owl/EVS/ComplexProperties.xsd#"><n0:def-definition>Irreversible serine proteinase inhibitors that exert their action on peptidases. Serpins can be localized inside, or outside of the cell, and are found in all groups of organisms with the exception of fungi. In human plasma, serpins represent approximately 2% of the total protein present.</n0:def-definition><n0:def-source>NCI</n0:def-source></n0:ComplexDefinition>
nci:P98
Some members of the serpin family do not undergo the S (stressed) to R (relaxed) conformational transition characteristic of active serpins. These family members exhibit no serine protease inhibitory activity. (UniProt)