Separation of two new trypsin-inhibiting fractions from human serum

Trace amounts of two unknown trypsin-inhibiting fractions have been separated from pooled human serum by DEAE-Sephadex chromatography. They are immunologically different from alpha1-antitrypsin, alpha2-macroglobulin or inter-alpha-trypsin inhibitor and they form two well separated peaks after rechromatography on DEAE-Sephadex column. Both of these fractions also inhibit chymotrypsin but not elastase. Their relation to other trypsin inhibitors of human serum is discussed.