Electrophoretic investigations of acid-stable proteinase-inhibitory activity in human serum

By means of a sensitive semiquantitative electrophoretic technique involving tryptic digestion of immobilized casein embedded in agarose gel, the acid-stable proteinase-inhibitory fraction of human serum was shown to consist of two fractions with alpha 1- and prealbumin mobility, respectively. The prealbumin-like migrating inhibitor (pA-PI) was previously thought to be the only inhibitor present in the acid supernatant. The pA-PI was demonstrated in native serum as well, but was not recovered quantitatively upon acid precipitation. Using antibody-containing intermediary gels pA-PI was shown to react with inter-alpha-trypsin inhibitor antibodies, whereas the alpha 1-inhibitor reacted with alpha 1-proteinase inhibitor antibodies. The pA-PI activity was compared to serum levels of creatinine and C-reactive protein using a limited number of patients. The inhibitor level was clearly increased in patients with high serum creatinine and in some cases of high concentrations of C-reactive protein in the serum. Only small amounts of pA-PI were detected in sera of healthy people.