Effects of neutral proteases from human leukocytes on structure and biological properties of human factor VIII

Human factor VIII was purified from cryoprecipitate and incubated for up to 24 hours with four neutral proteases of human blood leukocytes, namely, with elastase-like protease (ELP), chymotrypsin-like protease (CLP), collagenase and gelatinase. Electrophoretic patterns showed a reproducible sequence of degradation of factor VIII and of its 230,000 molecular weight subunit by ELP and CLP. Intermediate products were similar but those resulting from exhaustive proteolysis by ELP and CLP differed distinctly from each other. Procoagulant activity of factor VIII was rapidly and completely destroyed by ELP and CLP before visible electrophoretic changes would be detected. No increase in this activity was observed prior to its destruction. Von Willebrand factor (ristocetin cofactor) activity was considerably more resistant to ELP and CLP and declined in rough relation to degradation of highly aggregated forms of factor VIII. ELP and CLP produced a pronounced progressive increase in the Laurell reaction antigen. Normal human plasma showed a high potency to inhibit ELP and CLP. Large doses of these enzymes (300 microgram per ml) produced in the plasma medium only a moderate fall in factor VIII procoagulant activity. Collagenase and gelatinase did neither degrade factor VIII nor change its biological properties.