The effect of C̄l̄ inhibitor upon Hageman factor autoactivation

Abstract

Using components purified from human plasma, we have examined the effects of C̄l̄ Inhibitor (C̄l̄ INH), the primary inhibitor of activated Hageman Factor (HFa) and Hageman factor fragment (HFf), on Hageman Factor (HF) autoactivation. When Hageman factor was exposed to a negatively charged sulfate, provided by either a glass cuvette or dextran sulfate, the addition of C̄l̄ INH gave a dose-dependent inhibition of the activity observed. The ability of C̄l̄ INH to decrease the maximal enzymatic activity generated was markedly temperature dependent with inhibition increasing as the temperature was raised from 4°C to 37° C. Although the rates of both autoactivation and inhibition were decreased at lower temperatures (4° C), the latter rate was more sensitive to temperature modulation. When HF (final concentration 1 μmol/L) was incubated with C̄l̄ INH (0.54, 1.07, and 2.14 μmol/L) in the absence of an initiating surface, no increases in enzymatic activity were observed for up to 48 hours regardless of the C̄l̄ INH concentration. However, SDS polyacrylamide gel electrophoresis of the incubation mixture revealed that HF autodigestion had occurred by 48 hours despite the presence of C̄l̄ INH. In addition, the appearance of a new band suggested that a complex had been formed between the inhibitor and activated HF. Our findings indicate that C̄l̄ INH does not prevent HF autoactivation but rather inactivates the products of HF autodigestion.