A further alpha-protease inhibitor system, PI4, was detected in porcin
e sera using either 2D agarose gel, pH 5.0-PAGE, pH 9.0, or 1D PAGE fo
llowed by immunoblotting with rabbit anti-porcine PI2 or PI3 antisera.
PI4 inhibited chymotrypsin, but not trypsin. Seven allelic variants o
f PI4 were described. By haplotyping of alpha-protease inhibitor syste
ms in 52 complete families it was shown that PI4 locus belongs to the
PI gene cluster. The probable order of the PIloci was: PI1, PO1A, PI2,
PI4, PI3.