Polymorphic serum prealbumin (Pa) of pig, identified as and alpha1-protease inhibitor. 
Pig serum proteins were analysed by horizontal polyacrylamide gel electrophoresis, with a discontinuous buffer system (pH 9.0).  A 12% acrylamide concentration in the separation gel was used.  Each of the two paralbumin (Pa) alleles gave rise to two closely migrating fractions.  The polymorphic Pa was identified as an alpha1-protease inhibitor as the Pa fractions inhibited the esterolytic activity of both bovine trypsin and chymotrypsin.  Therefore, it has been proposed that the locus symbol for this prealbumin be changed to Pi-1.  The protease inhibitory spectra and electrophoretic mobility of the Pa (Pi-1) fractions suggested that this protein was probably the same as the pig serum alpha1-protease inhibitor described in some earlier studies and that it corresponds to human serum alpha 1-protease inhibitor (Pi).