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Lipoprotein a inhibits streptokinase-mediated activation of human plasminogen
J M Edelberg1, M Gonzalez-Gronow, S V Pizzo
1Department of Pathology, Duke University Medical Center, Durham, North Carolina 27710.
Abstract:
Lipoprotein a [Lp(a)] inhibits human plasminogen (Pg) conversion to plasmin (Pm) by streptokinase- (SK-) mediated activation. Kinetic and binding studies indicate that Lp(a) inhibits Pg activation by competitive and uncompetitive inhibition. Lp(a) competes with Pg for SK and forms a stable complex. Lp(a) does not, however, inhibit Pg activation by the proteolytic SK-Pm complex. The SK-Pg and SK-Pg(act) intermediate complexes are possible targets of the Lp(a) uncompetitive inhibition. The competitive inhibition constant (Kic) is 45 nM or 14 mg/dL, and the uncompetitive inhibition constant (Kiu) is 140 nM or 42 mg/dL, corresponding to physiologic and pathophysiologic Lp(a) concentrations, respectively.