EFFECTS OF FIBRIN AND ALPHA(2)-ANTIPLASMIN ON PLASMINOGEN ACTIVATION BY STAPHYLOKINASE

Staphylokinase obtains plasminogen activating activity by forming a co mplex with plasminogen, Although the enzymatic activity of staphylokin ase is enhanced by fibrin, how fibrin enhances enzymatic activity has not been determined yet. The effects of fibrin, or fibrinogen fragment s, on the activation of plasminogen by staphylokinase was investigated using CNBr-digested fibrinogen fragments (FCB-2 and FCB-5) and plasmi n-degraded cross-linked fibrin fragments ((DD)E complex, Do fragments and E fragments). Kinetic analysis of the activity of staphylokinase r evealed that its plasminogen activating activity, which was expressed as kcat/Km, was enhanced by FCB-2 (10-fold) and FCB-5 (5-fold). These fibrin fragments caused 38-, 30-, and 8.5-fold increases in activity f or the DD fragment, (DD)E complex and E fragment, respectively, Althou gh alpha(2)-antiplasmin inhibited the activation of plasminogen by sta phylokinase, FCB-5 abolished its inhibitory effects, and the plasminog en activating activity of staphylokinase was restored. The inhibitory effects of alpha(2)-antiplasmin on the activation of mini-plasminogen by staphylokinase were less than for Glu- or Lys-plasminogen, and the inhibitory effect of alpha-antiplasmin was not altered by fibrin or EA CA. These findings indicate that the staphylokinase/plasmin(ogen) comp lex reacts with fibrin even in the presence of alpha(2)-antiplasmin, a nd efficient plasminogen activation takes place on the surface of fibr in. (C) 1996 Wiley-Liss, Inc.