NCIt 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.;
NCIt note : 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);