Hageman factor fragment inhibitor in corn seeds: Purification and characterization

A specific, potent inhibitor of Hageman factor fragment (HF f) was isolated from sweet corn kernels. Three variants with pI's of 5.1, 6.3, and 7.7, and M r 11,000–14,000 were found. The corn HF f inhibitor (CHFI) forms a 1:1 molar complex with HF f or trypsin, and prolongs the activated partial thromboplastin time of human plasma. The K i of CHFI 6.3 with HF f was 2.4 × 10 -8 M. CHFI does not inhibit human plasma or urinary kallikreins, plasmin, α-thrombin, hog pancreatic kallikrein, bovine Factor X a or α-chymotrypsin. CHFI appears to be identical with the corn trypsin inhibitor (CTI) previously reported (Swartz et al., J. Biol. Chem. 252 , 8105, 1977). The corn inhibitor is unique in its strong inhibition of HFf and very narrow spectrum of inhibition of other serine proteinases.