[Binding of Glu-plasminogen by fibrinogen and byproducts of its proteolysis].

The ability of the native form of plasminogen (Glu-plasminogen) to form complexes with fibrinogen and its fragments immobilized on CNBr-agarose was studied. It was found that unlike Lys-plasminogen, the native form of the proenzyme does not bind to fibrinogen agarose. Limited proteolysis of fibrinogen by plasmin involving alpha C-domains results in the appearance of Glu-plasminogen binding sites at fibrinogen surface. The X2 fragment of fibrinogen binds to about 0.5 moles of Glu-plasminogen at an equimolar ratio of the interacting proteins. Under these conditions, the amount of bound Glu-plasminogen does not increase as a result of subsequent hydrolysis of fibrinogen down to end products, fragments E and D. It was found that Glu-plasminogen interacts with both E- and D-fragments of fibrinogen. Similar to Lys-plasminogen, Glu-plasminogen exhibits a high affinity for the E-fragment. The maximal quantity of the bound protein under the given experimental conditions is 2 moles per mole of the immobilized E-fragment. The interaction of Glu-plasminogen with the E-fragment is mediated by the lysine-binding sites of the proenzyme with a high and low affinity [Kd = 1.8.10(-6) and 7.5.10(-5) M, respectively]. Glu-plasminogen, unlike Lys-plasminogen, shows a low affinity for the D-fragment (Kd = 2.10(-5) M). Glu-plasminogen cannot be adsorbed by arginine-binding sites at the DH fragment-agarose.