HEPARIN AND HEPARAN-SULFATE ENHANCEMENT OF THE INHIBITORY ACTIVITY OFPLASMINOGEN-ACTIVATOR INHIBITOR TYPE-1 TOWARD UROKINASE-TYPE PLASMINOGEN-ACTIVATOR

To study effects of glycosaminoglycan on the interaction between two c hain urokinase type plasminogen activator (tcu-PA) (EC 3.4.21.31) and plasminogen activator inhibitor type 1 (PAI-I) the second order rate c onstant (k(1)) between high molecular weight tcu-PA and active recombi nant prokaryotic PAI-1 (rpPAI-1) was determined employing a continuous method using chromogenic substrate S-2444 either in the presence or a bsence of various kinds of glycosaminoglycans. k(1) was (5.9 +/- 1.6) 10(6)/mol per s in the absence of effector molecule, and following add ition of heparin (1.0 U/ml) k(1) was enhanced to (3.22 +/- 0.73).10(7) . A significant enhancement of k(1) was also obtained by heparan sulfa te (1.87 +/- 0.25).10(7). Dermatan sulfate or chondroitin sulfate did not show a significant effect on k(1) although a slight decrease was o btained by mono-dextran sulfate (4.2 +/- 1.2).10(6). The intrinsic flu orescence of rpPAI-1 was shown to be slightly increased following addi tion of heparin (1.49 +/- 0.22%, n = 6), suggesting that heparin may e nhance the inhibitory activity of PAI-1 toward tcu-PA both by a templa te mechanism and by a modification of PAI-1 structure.