Plasma glycoprotein member of the serpin superfamily which inhibits TRYPSIN; NEUTROPHIL ELASTASE; and other PROTEOLYTIC ENZYMES. Commonly referred to as alpha 1-proteinase inhibitor (A1PI), it exists in over 30 different biochemical variant forms known collectively as the Pi (protease inhibitor) system. Hereditary A1PI deficiency is associated with PULMONARY EMPHYSEMA.
