Synthesis and fibrinolytic activity of anti-CR1/tPA and IgG/tPA conjugates. (A) Modification curves of anti-CR1 IgG and tPA at indicated molar ratios (Mr) of SATA and SMCC, respectively, determined with Ellman reagent. (B) In vitro lysis of ¹²⁵I-fibrinogen clots by 5 nM tPA or SMCC-modified tPA. (C) In vitro fibrinolysis of ¹²⁵I-fibrinogen clots by indicated amounts of tPA or tPA conjugates. The data in this and the following figures are presented as the mean plus or minus SEM. Unless specified otherwise, in vitro fibrinolysis data show results of triplicates for each condition. The insert shows anti-CR1/tPA analysis using a 4% to 12% gradient SDS-PAGE run in Tris-Glycine buffer under nonreducing conditions. The results show maternal anti-CR1 IgG (left band) and the anti-Cr1/tPA conjugate (right band) containing species with 1, 2, or 3 molecules of tPA per molecule of IgG.