INTERACTION BETWEEN STAPHYLOKINASE, PLASMIN(OGEN), AND ALPHA-2-ANTIPLASMIN - RECYCLING OF STAPHYLOKINASE AFTER NEUTRALIZATION OF THE PLASMIN-STAPHYLOKINASE COMPLEX BY ALPHA-2-ANTIPLASMIN

Although the plasminogen activating equimolar complex of staphylokinas e (STA) with human plasmin is very rapidly inhibited by alpha2-antipla smin, STA is a potent fibrinolytic agent in a human plasma milieu whic h contains 1 muM alpha2-antiplasmin. In the present study, it was foun d that the complex of plasmin with recombinant STA (STAR), after neutr alization with alpha2-antiplasmin, retained the full plasminogen activ ating potential of STAR when added to a plasminogen solution (93 +/- 5 % residual activity). When added to human plasma containing a I-125-fi brin-labeled plasma clot, equi-effective concentrations (causing 50% l ysis in 2 h) were 17 +/- 3.0, 13 +/- 1.0, and 20 +/- 1.0 nM for STAR, equimolar plasmin-STAR mixtures, and plasmin-STAR mixtures neutralized by alpha2-antiplasmin, respectively. Gel filtration of mixtures of pl asmin(ogen) and STAR revealed elution as plasmin-STAR complex (M(r) al most-equal-to 100,000), whereas after addition of alpha2-antiplasmin, STAR eluted with an apparent M(r) of 20,000. When mixtures of plasmin and STAR were adsorbed to lysine-Sepharose, STAR adsorbed quantitative ly (96 +/- 1%) to the gel, whereas it was nearly quantitatively recove red in the unbound fraction (92 +/- 4%) after addition of alpha2-antip lasmin to the mixture. Scatchard analysis of the binding of STAR to pl asmin-Sepharose yielded a dissociation constant of 55 nM, whereas no s pecific binding of STAR to plasmin-alpha2-antiplasmin-Sepharose could be demonstrated. These findings indicate that, both in purified system s and in a human plasma milieu containing a I-125-fibrin-labeled plasm a clot, neutralization of the plasmin-STAR complex by alpha2-antiplasm in results in dissociation of functionally active STAR from the comple x and recycling of STAR to other plasminogen molecules. This dissociat ion-recycling process may explain the high fibrinolytic potency of STA R in a plasma milieu in the presence of high concentrations of alpha2- antiplasmin.