Interaction of plasminogen activator of urokinase type with human serum

: Effects of blood serum on u-PA (EC 3.4.21.31) fibrinolytic activity were studied. After incubation for one hour at 37 degrees of the enzyme with human blood serum (55-145 IU/ml of blood serum) the enzymatic activity was completely inhibited. At the same time, amido-lytic activity of u-PA, estimated with low molecular substance S2444 as a substrate, was maintained in presence of blood serum. Blood serum inhibitors did not exhibit the specific affinity to u-PA. Serine proteases (trypsin, chymotrypsin and plasmin) competed with u-PA at equimolar concentrations. These inhibitors were inactivated after blood serum preincubation with primary amines methylamine, ethylamine, putrescine, spermidine and spermine (0.1-10 mM). The u-PA-inhibitor complexes were not dissociated in presence of 2.5 mM sodium dodecylsulfate. Trypsin-albumin copolymer bound specifically the blood serum u-PA inhibitors and the fraction adsorbed was electrophoretically characterized as a protein with molecular mass of 185 kDa.