A B S T R A C T An asymptomatic woman (Ms. \Vil-liams) was found to have a severe abnormality in the surface-activated intrinsic coagulation, fibrinolvtic, and kinin-generating pathways. Assays for known coagulation factors were normal while Fletcher factor (prekallikrein) was 45%, insufficient to account for the observed markedly prolonged partial thromboplastin time. Plasminogen proactivator was present at 20% of normal levels and addition of highly purified plasminogen proactivator containing 10% plasminogen activator partially corrected the coagulation and fibrinolytic abnormalities but not the kinin-generating defect. This effect was due to its plasminogen activator content. In addition, Williams trait plasma failed to convert prekallikrein to kallikrein or release kiniin upon incubation with kaolin. Kininogen

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A B S T R A C T The activation and function of surfacebound Hageman factor in human plasma are dependent upon both high molecular weight (HMW) kininogen and prekallikrein. HMW kininogen does not affect the binding of Hageman factor to surfaces, but it enhances the function of surface-bound Hageman factor as assessed by its ability to activate prekallikrein and Factor XI. The initial conversion of prekallikrein to kallikrein by the surface-bound Hageman factor in the presence of HMW kininogen is followed by a rapid enzymatic activation of Hageman factor by kallikrein. The latter interaction is also facilitated by HMW kininogen. Kallikrein therefore functions as an activator of Hageman factor by a positive feedback mechanism and generates most of the activated Hageman factor during brief exposure of plasma to activating surfaces. HMW kininogen is a cofactor in the enzymatic activation of Hageman factor by kallikrein and it also augments the function of the activated Hageman factor generated. The stoichiometry of the Hageman factor interaction with HMW kininogen suggests that it enhances the activity of the active site of Hageman factor. Since HMW kininogen and prekallikrein circulate as a complex, HMW kininogen may also place the prekallikrein in an optimal position for its reciprocal interaction with Hageman factor to proceed. The surface appears to play a passive role upon which bound Hageman factor and the prekallikrein-HMW kininogen complex can interact.H. L. Meier is a Predoctoral fellow,

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1Four radioactive kallikreins were isolated from rat kidney slices incubated with [3H -Lleucine.2 The kallikreins were purified by procedures previously used for the isolation of rat urinary kallikreins (Nustad & Pierce, 1974), and by affinity chromatography on a column of insolubilized anti-rat urinary kallikrein. 3 The kidney kallikreins resembled the urinary kallikreins in their relative amounts, isoelectric points and electrophoretic mobilities on polyacrylamide disc gels. 4 The data indicate that the kidney synthesizes four kallikreins which are released into urine. The kallikreins are not changed by passage through the lower urinary tract.