Interaction of Factor XI and Kallikrein with High Molecular weight Kininogen

The molecular weight (mol. wt.) of factor XI in normal plasma fractionated on Sephadex G-200 was over 400,000, while the mol. wt. of factor XI in HMW kininogen deficient plasma was 175,000. When HMW kininogen deficient plasma was made 70 μg/ml in HMW kininogen and fractionated on Sephadex G-200, factor XI was again found at mol. wt.~ 400,000. Prekallikrein was found complexed to HMW kininogen (Mandle and Kaplan PNAS 73: 4179, 1976) however, no complex containing both prekallikrein and factor XI was identified and neither Hageman factor nor plasminogen were complexed to HMW kininogen. Gel filtration of normal plasma had a major peak of HMW kininogen at mol. wt. of 200,000 while isolated HMW kininogen had a mol. wt. of 130,000 on reduced SDS gels (SDS-PAGE). Alkaline disc gel electrophoresis of HMW kininogen revealed two bands of equal intensity and each possessed the ability to correct the coagulation defect of HMW kininogen deficient plasma. Digestion of HMW kininogen with kallikrein generated bradykinin and a peptide of mol. wt. 13,000, while SDS-PAGE of the residual HMW kininogen revealed bands of mol. wt.110,000 and 120,000. Upon reduction, bands at mol. wts. 77,000, 66,000, and 37,000 were obtained. Antibody specific for HMW kininogen reacted with either native or kallikrein-treated HMW kininogen but not reduced, kinin-free kininogen. Kinin-free kininogen, reduced kinin-free kininogen, and the major fragment eluted from alkaline disc gels after electrophoresis of reduced kinin-free kininogen all retained coagulant activity. Factor XI as well as prekallikrein therefore circulate complexed to HMW kininogen; these complexes may then interact with surface-bound Hageman factor. Kallikrein digests human HMW kininogen to yield bradykinin, a peptide, and disulfide-linked fragments which retain functional activity.