Interaction of Plasminogen Activators and Plasminogen with Heparin: Effect of Ionic Strength

Abstract

SummaryIn order to define the possible effects of heparin on the fibrinolytic system under physiological conditions, we studied the interactions of this drug with plasminogen and its activators at various ionic strengths. As reported in recent literature, heparin stimulated the activation of Lys-plasminogen by high molecular weight (HMW) and low molecular weight (LMW) two-chain urokinase-type plasminogen activator (u-PA) and two-chain tissue-type plasminogen activator (t-PA) 10- to 17-fold. Our results showed, however, that this stimulation only occurred at low ionic strength and was negligible at a physiological salt concentration. Direct binding studies were performed using heparin-agarose column chromatography. The interaction between heparin and Lys-plasminogen appeared to be salt sensitive, which explains at least in part why heparin did not stimulate plasminogen activation at 0.15 M NaCl. The binding of u-PA and t-PA to heparinagarose was less salt sensitive. Results were consistent with heparin binding sites on both LMW u-PA and the amino-terminal part of HMW u-PA. Single-chain t-PA bound more avidly than two-chain t-PA. The interactions between heparin and plasminogen activators can occur under physiological conditions and may modulate the fibrinolytic system.

The effect of fucoidan, heparin and cyanogen bromide-fibrinogen on the activation of human glutamic-plasminogen by tissue plasminogen activator

“…Most of the above studies were performed at subphysiological ionic strengths of buffers and the results were inconsistent because of the variations in the ionic strengths of the buffers used. Interaction of heparin with Lys-plasminogen was reported to be salt sensitive while binding of t-PA to heparin-agarose was less salt sensitive [27]. Glu-Plg, but not t-PA, was reported to bind with fucoidan-sepharose [19].…”

“…Recent studies by Liang et al [26] suggested that the stimulation of t-PA activity by heparin was probably due to a direct binding of heparin to t-PA, causing a conformational change of t-PA and making it more accessible to plasminogen interaction. Single chain t-PA is reported to bind with high affinity to heparin-agarose [27] and the heparin binding sites on t-PA have been located on the finger and kringle 2 domains [36]. The results of affinity chromatography using fucoidan-Sepharose showed a high degree of affinity between fucoidan and Glu-Plg while t-PA did not bind with fucoidan-Sepharose [19].…”

“…A detailed study on the effect of ionic strength of the buffer on the interaction of plasminogen activators such as t-PA, and HMW u-PA and plasminogen with heparin was reported [27]. Increasing the ionic strength of the buffer by adding 0.05 mol/l sodium chloride significantly decreased the enhancement by heparin and at a final concentration of 0.125 mol/l NaCl, the stimulatory effect of heparin was entirely eliminated [27].…”

“…A detailed study on the effect of ionic strength of the buffer on the interaction of plasminogen activators such as t-PA, and HMW u-PA and plasminogen with heparin was reported [27]. Increasing the ionic strength of the buffer by adding 0.05 mol/l sodium chloride significantly decreased the enhancement by heparin and at a final concentration of 0.125 mol/l NaCl, the stimulatory effect of heparin was entirely eliminated [27]. 6-Aminohexanoic acid (6-AH) was reported [28][29][30] to alter the gross conformation of GluPlg by binding of the amino acid to one or more of its weak binding sites, and was also reported [31] to reverse the chloride-induced tight conformation of GluPlg.…”

Regulation of Urokinase/Urokinase Receptor Interaction by Heparin-like Glycosaminoglycans

“…u-PA does not contain the typical HP-binding consensus sequence reported by Cardin and Weintraub (15), although it seems to bind to HP through the kringle domain of its aminoterminal fragment (ATF), where several basic amino acid residues are found (16 -19). There is also evidence that the u-PA B-chain and the u-PA catalytic site participate in u-PA/HP interactions (19,20). Moreover, injection of HP in mice increases the fibrinolytic activity in the plasma euglobulin fraction by an increase of u-PA protein levels, probably following u-PA elution from endothelial cells (21).…”