[Studies on the properties of the component of plasmin-treated IgG and the relation between IgG aggregates and complement-fixing ability (author's transl)].

No distinct differences were noted in the components of plasmin-treated IgG from the known components of papain-treated IgG (Fab and Fc fragments and untreated IgG) on the physicochemical and the immunological properties and the biological activities. Incubation of IgG with 30 cu/g of plasmin for 96 hours at 20 degrees C was found to be optimum. The plasmin-treated IgG by this condition, which gives complement-fixing ability (C'H50) below 23, did not show blood pressure depression, i.e. below 10% for dogs. Three components (Pl-Fab, Pl-Fc and Pl-IgG) were isolated from the plasmin-treated IgG by gel filtration on Sephadex G200 and CM-cellulose column chromatography. The Pl-Fc and the Fc isolated from the papain-treated IgG were obtained in crystalline forms. The extinction coefficients at 280 nm were 14.0 (IgG), 14.2 (Pl-Fab) and 14.1 (Pl-Fc). The molecular weights were 163,000, 58,000 and 54,000 and the S20,w values were 6.82, 3.82 and 3.77 for Pl-IgG, Pl-Fab and Pl-Fc, respectively. These three components were identical with IgG, Fab and Fc, respectively, on the electrophoretic and the immunological demonstrations. The titer of complement-fixation of IgG was decreased from 49 to 19 by plasmin treatment, however, it was retained at low level even in each isolated component. Whe 7S IgG was incubated at 37 degrees C, reaggregation was observed, as generally understood accompanying by elevated complement-fixing ability. Whereas it was noticed after long-term incubation of plasmin-treated IgG that the changes of complement-fixing ability could occur independently from the amount of aggregates. This fact was clearly revealed on the experiments in which IgG was treated at pH 3 in glycine buffer solution.