The hyaluronic acid binding serine protease (PHBSP), an enzyme with the ability to activate the coagulation factor FVII and the plasminogen activator precursors and to inactivate factor VIII and factor V, could be isolated from human plasma in the presence of 6M urea as a single-chain zymogen, whereas under native conditions only its activated two-chain form was obtained. The total yield of proenzyme (proPHBSP) was 5-6 mg/l, corresponding to a concentration of at least 80-100nM in plasma. Upon removal of urea, even in the absence of charged surfaces a rapid development of amidolytic activity was observed that correlated with the appearance of the two-chain enzyme. The highest activation rate was observed at pH 6. ProPHBSP processing was concentration-dependent following a second order kinetic and was accelerated by catalytic amounts of active PHBSP, indicating an intermolecular autocatalytic activation. Charged macromolecules like poly-L-lysine, heparin, and dextran sulfate strongly accelerated the autoactivation, suggesting that in vivo proPHBSP activation might be a surface-bound process. The intrinsic activity of the proenzyme was determined to be 0.25-0.3%, most likely due to traces of PHBSP. The presence of physiological concentrations of known plasma inhibitors of PHBSP, like alpha2 antiplasmin and C1 esterase inhibitor, but not antithrombin III/heparin, slowed down zymogen processing. Our in vitro data suggest that the autoactivation of proPHBSP during plasma fractionation is induced by the removal of inhibitors of PHBSP and is accelerated by charged surfaces of the chromatographic resins.

Further research is required to elucidate whether gemycircularviruses can infect humans or are indicative of contamination occurring during phlebotomy, plasma pool processing, or ongoing donor fungal infections.

Kallikrein and FXIa are the major contaminants in IVIGs. FXIa was highly procoagulant, with highest level in TEE-associated IVIGs. Since the NAPTT unambiguously identified FXIa procoagulant activity in IVIGs, its implementation as a release test would improve the safety of IVIGs.

A novel serine protease (PHBSP) was purified from human plasma by two chromatographic steps with a final yield of 1.6 mg/l plasma. The protease consists of two disulfide-bridged chains of about 50 and 30 kDa with the light chain containing the active site of the enzyme. NH 2 -terminal sequence analysis revealed identity to the deduced amino acid sequence of HGFA-like mRNA. The activity of PHBSP is strongly dependent on Ca 2+ ions and is efficiently inhibited by K K 2 -antiplasmin and aprotinin. Possible functions of PHBSP in the hemostatic system are discussed.z 1999 Federation of European Biochemical Societies.

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