Immunochemical characterization of human plasminogen activators

Abstract

The high and low molecular mass forms of human urokinase (high M r urokinase and low M r urokinase) were purified to homogeneity and the human vascular plasminogen activator was partially purified. The urokinase molecules were radiolabelled with 125-iodine and assays of radioimmune binding and inhibition of binding were carried out. The high M r form was almost as good an inhibitor as the low M r form in the binding reaction between radiolabelled low M r urokinase and specific antibody, indicating that the low M r urokinase is a part of the high M r urokinase. This inhibition could be only partly reversed, indicating that the high M r urokinase has immunological determinants which are not present on the low M r urokinase. The human vascular plasminogen activator preparation partly inhibited the urokinase binding reactions. Contaminating proteins could be responsible for this inhibitory effect. Various human sera inhibited the binding reaction between the two forms of urokinase and antibody, indicating that normally either urokinase or an immunologically cross-reacting molecule is present in human sera. The inhibitory capacity of sera from patients with neoplastic disease was not different from that of other sera.