The mechanism of activation of plasminogen at the fibrin surface by tissue-type plasminogen activator in a plasma milieu in vitro. Role of alpha 2-antiplasmin.
The mechanism of activation of human Glu-plasminogen by fibrin-bound tissue-type plasminogen activator (t-PA) in a plasma environment or in a reconstituted system was characterized. A heterogeneous system was used, allowing the setting of experimental conditions as close as possible to the physiological fibrin/plasma interphase, and permitting the separate analysis of the products present in each of the phases as a function of time. The generation of plasmin was monitored both by spectrophotometric analysis and by radioisotopic analysis with a plasmin-selective chromogenic substrate and radiolabelled Glu-plasminogen respectively. Plasmin(ogen)-derived products were identified by SDS/PAGE followed by autoradiography and/or immunoblotting. When the activation was performed in a plasma environment, the products identified on the fibrin surface were Glu-plasmin (90%) and Glu-plasminogen (10%), whereas in the soluble phase only complexes between Glu-plasmin and its fast-acting inhibitor were detected. Identical results were obtained with a reconstituted system comprising solid-phase fibrin, t-PA, Glu-plasminogen and and alpha 2-antiplasmin. In contrast, when alpha 2-antiplasmin was omitted from the solution, Lys-plasmin was progressively generated on to the fibrin surface (30%) and released to the soluble phase. In the presence of alpha 2-antiplasmin or in plasma, the amount of active plasmin generated on the fibrin surface was lower than in the absence of the inhibitor: in a representative experiment the initial velocity of plasmin generation was 2.8 x 10(-3), 2.0 x 10(-3) and 1.8 x 10(-3) (delta A405/min) for 200 nM-plasminogen, 200 nM-plasminogen plus 100 nM-alpha 2-antiplasmin and native plasma respectively. Our results indicate that in plasma or in a reconstituted purified system containing plasminogen and alpha 2-antiplasmin at a ratio similar to that found in plasma (1) the activation pathway of native Glu-plasminogen proceeds directly to the formation of Glu-plasmin, (2) Lys-plasminogen is not an intermediate of the reaction and therefore (3) Lys-plasmin is not the final active product. However, in the absence of the inhibitor, Lys-plasmin and probably Lys-plasminogen, which is more readily activated to plasmin than is Glu-plasminogen, are generated as well.
Rouy
D
D
Institut National de la Santé et de la Recherche Médicale, Hôpital de Bicêtre, France.
Anglés-Cano
E
E
D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation / Q000187:drug effects; D005337:Fibrin / Q000378:metabolism*; D005341:Fibrinolysin / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D015151:Immunoblotting; D007700:Kinetics; D010446:Peptide Fragments / Q000378:metabolism; D010958:Plasminogen / Q000378:metabolism*; D013053:Spectrophotometry; D010959:Tissue Plasminogen Activator / Q000494:pharmacology*; D000511:alpha-Macroglobulins / Q000502:physiology*
D010446:Peptide Fragments; D000511:alpha-Macroglobulins; C033809:lys-plasmin; C018998:lysyl-plasminogen; C024668:plasmin-alpha(2)-macroglobulin complex; D005337:Fibrin; D010958:Plasminogen; D010959:Tissue Plasminogen Activator; D005341:Fibrinolysin