Part of prekallikrein removed from human plasma together with IgG - immunoblot experiments and functional tests

With the present study, evidence is provided that prekallikrein (PK) in hum an plasma might be present in two different states, one of them removed alo ng with IgG on Protein G columns. At a plasma dilution of 1 + 2.5, small am ounts of an IgG fraction were left in plasma along with all of the PK. At a dilution of 1 + 11, nearly all IgG was removed. The removal in parallel of part of the PK was shown in immunoblot experiments and confirmed in amidas e assays. One monoclonal antibody against PK (13G11) and two preparations o f polyclonal antibodies were used for the immunoblot experiments. Different peptide substrates (S-2302, S-2222, Bz-Pro-Phe-Arg-pNA), along with protea se inhibitors (soybean trypsin inhibitor, corn trypsin inhibitor, lima bean trypsin inhibitor) were used for the amidase assays. The amidase assays in dicated that factors XII and XI were reduced by Protein G columns. In all e xperiments with extensive removal of IgG, protein recognized by the factor XII light chain mAb C6B7 was removed at the same time. This antibody prepar ation did not detect purified contact factors, but it did recognize a prepa ration of purified beta-FXIIa, and also significant amounts of protein pres ent in plasma deficient in factor XII and not detectable in plasma deficien t in PK. This protein accordingly seems to be connected with the PK fractio n removed with IgG.