title: Control of human plasminogen activation.
abstract: The activation of Glu1-plasminogen (Glu-Pg) by streptokinase (SK), urokinase (UK) and tissue plasminogen activator (tPA) is under rigorous control by molecules such as epsilon-aminocaproic acid (EACA), fibrinogen (Fg), fibrin (Fn) and, as we have recently discovered, anions. This presentation will focus on the biochemical mechanisms that are involved in these processes. In the case of activation by SK, a species of activator complex, composed of Glu-Pg and SK, can be identified that is inhibited by anions, such as Cl-, and stimulated by Fg and Fn. This species rapidly decays to another activator complex, also consisting of Glu-Pg and SK, that is much less sensitive to control by these effector molecules. The most stable activator complex, containing equimolar SK and plasmin, is not affected to a great extent by anions, Fg or Fn. In the overall activation of Glu-Pg by SK, Cl- behaves as a mixed inhibitor, with a Ki of 6.4-9.2 mM, and Fg functions as a mixed activator, displaying a Ka of 110-240 nM. These results show that activation of Glu-Pg by SK in physiological samples would be considerably inhibited by Cl- in the absence of Fg. The activation of Glu-Pg by both high- and low-molecular weight UK is also inhibited by Cl-, but is stimulated by EACA. The inhibition by Cl- does not occur in the presence of concentrations of EACA that saturate its weak binding sites on Glu-Pg, and the stimulation by EACA is maximally exhibited in the presence of Cl-.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D015119:Aminocaproic Acid / Q000494:pharmacology; D002712:Chlorides / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D007700:Kinetics; D010958:Plasminogen / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010960:Plasminogen Activators / Q000494:pharmacology*; D013300:Streptokinase / Q000494:pharmacology; D010959:Tissue Plasminogen Activator / Q000494:pharmacology; D014568:Urokinase-Type Plasminogen Activator / Q000494:pharmacology
chemical_list: D002712:Chlorides; D010958:Plasminogen; D013300:Streptokinase; D010960:Plasminogen Activators; D010959:Tissue Plasminogen Activator; D014568:Urokinase-Type Plasminogen Activator; D015119:Aminocaproic Acid