Tissue plasminogen activator catalyzed Lys-plasminogen activation on heparin-inserted phospholipid liposomes.
We prepared heparin-inserted phospholipid liposomes as a functional model of heparan sulfate present on the vascular surface and examined tissue plasminogen activator (t-PA) catalyzed plasminogen activation on the liposome surface. Kinetic analyses showed a marked increase in the affinity of t-PA for Lys-plasminogen in the presence of heparin-inserted phosphatidylcholine (PC) liposomes. The catalytic efficiency (kcat/Km) of t-PA for the plasminogen activation on the surface of heparin-inserted PC liposomes was 5.4 times that on the surface of heparin-free PC liposomes. This stimulatory action of immobilized heparin was apparently affected by changing the phospholipid component of liposomes. Phosphatidylethanolamine or stearylamine, having a positively charged group, reduced the catalytic efficiency of t-PA by raising its Km value (10-fold), whereas negatively charged phospholipids, phosphatidylserine and phosphatidylinositol, did not affect the efficiency. t-PA and generated plasmin bound to the liposome surface heparin were protected from inhibition by plasminogen activator inhibitor type 1 and alpha 2-plasmin inhibitor, respectively. t-PA-induced clot lysis of euglobulin or whole plasma, which contained native (Glu-) plasminogen and the above inhibitors, was also accelerated by addition of heparin-inserted PC liposomes. These results suggest that the vascular surface heparin-like molecules may play an important role in modulating fibrinolytic events. The principles of conjugation of t-PA with a biologically active liposome will be applied to the construction of better thrombolytic agents.
Soeda
S
S
Department of Biochemistry, Faculty of Pharmaceutical Sciences, Fukuoka University, Japan.
Sakaguchi
S
S
Shimeno
H
H
Nagamatsu
A
A
D055598:Chemical Phenomena; D002621:Chemistry; D004789:Enzyme Activation / Q000187:drug effects; D006493:Heparin; D006801:Humans; D008081:Liposomes; D008956:Models, Chemical; D010446:Peptide Fragments / Q000378:metabolism*; D010743:Phospholipids; D010958:Plasminogen / Q000378:metabolism*; D010959:Tissue Plasminogen Activator / Q000494:pharmacology*
D008081:Liposomes; D010446:Peptide Fragments; D010743:Phospholipids; C018998:lysyl-plasminogen; D010958:Plasminogen; D006493:Heparin; D010959:Tissue Plasminogen Activator