UROKINASE AND ITS COMPLEX WITH PLASMINOGEN-ACTIVATOR INHIBITOR-3 PROTEIN-C INHIBITOR IN URINE

Urokinase-type plasminogen activator (u-PA) occurs either in a single- chain form or in a two chain form (scu-PA or tcu-PA, respectively). Th e occurrence of the different forms of u-PA and the formation of u-PA- inhibitor complexes was studied in urine samples from 10 healthy donor s. Measurement by means of a bio-immunoassay showed that the urine sam ples contained 307 +/- 189 ng/ml u-PA (mean +/- SD), of which 72 +/- 1 5% occurred in the active two chain form and 28 +/- 15% in the plasmin -activatable single chain form. SDS-polyacrylamide gel electrophoresis followed by fibrin zymography revealed that fresh urine contained no, or only traces of, u-PA-inhibitor complexes. In contrast to what has previously been published, the bulk of u-PA appeared to be in an uncom plexed 55kD form. Incubation of urine at 37 degrees C for 8h did not l ead to the formation of u-PA-inhibitor complexes. However, after rapid removal of the low molecular weight fraction of urine on a gel filtra tion column a 100kD complex, consisting of u-PA and plasminogen activa tor inhibitor-3/protein C inhibitor, was formed during incubation (t1/ 2 approximate to 45 min). Complex formation was dependent on stimulati on by urinary glycosaminoglycans and only occurred at a low ionic stre ngth, which explains why no complexes were formed in the untreated uri ne samples of healthy donors.