Western blot analyses of prekallikrein and its activation products in human plasma

Prekallikrein (PK), a zymogen of the contact system, and its activation products, kallikrein (KAL), KAL-inhibitor complexes and fragments containing KAL epitope(s) have been detected in human plasma by immunoblotting with a monoclonal anti-human plasma PK antibody, MAb 13G11. Detection of antigen-MAb 13G11 complexes with peroxidase-conjugated anti-IgG showed that the two variants of PK (85- and 88-kDa) are the only major antigen species in normal, non-activated plasma. Upon plasma activation with kaolin, the intensity of the PK bands decreased with formation of complexes of KAL with C1 inhibitor (C1 INH) and alpha 2-macroglobulin (alpha 2 M) identical to those formed by the purified proteins. Immunoblots of normal plasma showed good correlation between the PK detected and the amount of plasma assayed. Increasing amounts of KAL incubated with a constant volume of PK-deficient plasma showed increasing amounts of KAL and of KAL-C1 INH and KAL-alpha 2 M complexes. Complexes of KAL-antithrombin III (ATIII) and the ratio of KAL-alpha 2 M/KAL-C1 INH were higher in activated C1 INH-deficient plasmas than in activated normal plasmas. Protein resolution by 3-12% gradient SDS-PAGE and epitope detection with [125I]MAb 13G11 showed four KAL-alpha 2 M species and a 45-kDa fragment(s) in both surface-activated normal plasma and complexes formed by purified KAL and alpha 2 M. Immunoblots of activated plasma also showed bands at the position of KAL-C1 INH and KAL-ATIII complexes. When alpha 1-antitrypsin Pittsburgh (alpha 1-AT. Pitts) was added to plasma before activation, KAL-alpha 1-AT. Pitts was the main complex.(ABSTRACT TRUNCATED AT 250 WORDS)