Fibrin-binding urokinase (or precursor form of urokinase) with a molecular weight of about 100,000 in fresh human urine.

Fresh human urine was found to contain at least three different molecular forms of fibrin-binding urokinase (UK) or its precursor, all of which were absorbed on a fibrin/Celite column at neutral pH, and could be eluted with 0.3-1.0 mol/l NaCl in phosphate buffer, followed by 0.2 mol/l, Arg, 2 mol/l KSCN, and 2 mol/l urea, respectively. The main molecular form isolated revealed a molecular weight (MW) of approximately 100,000 (UK-100), and the minor ones were estimated to have MW of 150,000-200,000 and 45,000. In contrast, commercially obtained UK preparations contained mostly active enzymes with MW of 53,000 and 32,000, respectively, and the remaining high molecular forms represented less than 2.0% of the total amount. Rabbit monospecific antibody (IgG) against UK subcomponent (active heavy chain; H-chain UK) reacted and inhibited the fibrinolytic activity of all the active UK molecules. The UK-100 isolated was relatively stable in solution at neutral pH and resistant to mild reduction, without molecular change. Although the preparation had a very low specific activity (ca. 300 IU/mg protein), both the pyro-Glu-Gly-Arg-pNA amidolytic and plasminogen activating activities could be partially enhanced by the addition of trace amounts of plasmin. In this process, the appearance of two additional active enzymes of MW 53,000 and 32,000 was also confirmed by zymography.