title: Plasminogen activation by streptokinase via a unique mechanism.
abstract: The mechanism of human plasminogen (HPlg) activation by streptokinase (SK)-type activator was investigated with recombinant truncated SK peptides. An enzyme-substrate intermediate of HPlg.SK. HPlg ternary complex was demonstrated by a sandwich-binding experiment. Formation of the ternary complex was saturable, HPlg-specific, and inhibited by 6-aminocaproic acid. Three interaction sites between SK and HPlg were demonstrated. SK-(220-414) bound to HPlg with two binding sites: one to the micro-HPlg region, the catalytic domain of HPlg, and one to the kringle 1-5 region, with Kd values of 1.50 x 10(-7) and 2.44 x 10(-6) M, respectively. SK-(16-251) bound to a single site on the kringle 1-5 region of HPlg with a Kd of 4.09 x 10(-7) M. SK-(220-414) and SK-(16-251) competed for binding on the same or nearby location on the human kringle 1-5 domain. Combination of SK-(220-414) and SK-(16-251), but not either peptide alone, could effectively activate HPlg. In addition, SK-(16-251) dose-dependently enhanced the activation of HPlg by SK-(16-414), while the HPlg activation by SK-(16-414) was inhibited by SK-(220-414). We conclude that the HPlg that binds to the COOH-terminal domains of SK functions as an enzyme to catalyze the conversion of substrate HPlg that binds to the NH2-terminal domain of SK to human plasmin.
authors.affiliation: Department of Biochemistry, Medical College, National Cheng Kung University, Tainan, Taiwan 701, Republic of China.
authors.forename: K C
authors.initials: KC
authors.lastname: Young
authors.forename: G Y
authors.initials: GY
authors.lastname: Shi
authors.forename: D H
authors.initials: DH
authors.lastname: Wu
authors.forename: L C
authors.initials: LC
authors.lastname: Chang
authors.forename: B I
authors.initials: BI
authors.lastname: Chang
authors.forename: C P
authors.initials: CP
authors.lastname: Ou
authors.forename: H L
authors.initials: HL
authors.lastname: Wu
mesh_terms: D015119:Aminocaproic Acid / Q000494:pharmacology; D001665:Binding Sites; D001667:Binding, Competitive; D006801:Humans; D018082:Kringles; D010960:Plasminogen Activators / Q000494:pharmacology*; D011994:Recombinant Proteins / Q000494:pharmacology; D013300:Streptokinase / Q000494:pharmacology*
chemical_list: D011994:Recombinant Proteins; D013300:Streptokinase; D010960:Plasminogen Activators; D015119:Aminocaproic Acid