EFFECT OF PHENYLGLYOXAL-MODIFIED ALPHA(2)-ANTIPLASMIN ON UROKINASE-INDUCED FIBRINOLYSIS

One of the functions of activated blood clotting factor XIII (FXIIIa) is the crosslinking of alpha(2)-antiplasmin (alpha(2)AP) to fibrin. Th is process results in localization and concentration of alpha(2)AP thr oughout fibrin, thereby making fibrin more resistant to digestion by p lasmin. We reasoned that competition by chemically-modified inactive a lpha(2)AP (mod alpha(2)AP) with native alpha(2)AP would diminish the r esistance of fibrin to digestion by plasmin. Mod alpha(2)AP was prepar ed by treating native alpha(2)AP with an Arg-specific reagent, phenylg lyoxal. An average of four of the total nineteen Arg residues in alpha (2)AP reacted with phenylglyoxal and resulted in complete loss of plas min inhibitory activity; however, mod alpha(2)AP competed effectively with native alpha(2)AP for becoming crosslinked to fibrin by FXIIIa ca talysis. In the presence of mod alpha(2)AP: urokinase (UK)-induced pla sma clot lysis time shortened significantly. Mod alpha(2)AP enhanced U K-induced clot lysis in a whole blood system as shown by the similarit ies of rates of clot lysis for a mixture of 20 U/ml UK and 1.5 mu M mo d alpha(2)AP versus that induced by 100 U/ml UK without modo alpha(2)A P. Less fibrinog enolysis occurred in whole blood when mod alpha(2)AP was present since much lower UK concentrations were needed to achieve the same level of fibrinolysis than when only native alpha(2)AP was pr esent. Our results indicate that mod alpha(2)AP enhances UK-induced fi brinolysis by competitive inhibition of factor XIIIa-mediated incorpor ation of native alpha(2)AP into fibrin.