Detection of a novel plasma serine protease during purification of vitamin K-dependent coagulation factors.

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. NH2-terminal sequence analysis revealed identity to the deduced amino acid sequence of HGFA-like mRNA. The activity of PHBSP is strongly dependent on Ca2+ ions and is efficiently inhibited by alpha2-antiplasmin and aprotinin. Possible functions of PHBSP in the hemostatic system are discussed.