Purification and characterization of the biliary plasminogen activator bilokinase

The aim of the present study is to elucidate the enzymological and chemical properties of the plasminogen activator in bile, bilokinase. A bilokinase preparation was obtained from 94.2 liters of bovine gall bladder bile through seven purification steps, two of which employed a precipitation method in which ammonium sulfate and acetone were used sequentially. Twenty mg of bilokinase preparation with a specific activity of 5,900 IU/mg were obtained, for a 9% yield with 6,556-fold purification. This preparation revealed a single band upon disc electrophoresis. The bilokinase was a 3.32 S protein and its molecular weight was found to be 57,000. Isoelectric focusing showed that the bilokinase was separable into 5 fractions having different isoelectric points ranging from pH 7.4 to 9.0 The properties of the individual fractions have not yet been determined. The enzymatic activity of bilokinase was recognized to be heat-labile and to be stable at pH 4.0. The activation of plasminogen by bilokinase took place most effectively at pH 7.8 in a manner similar to that of urokinase. In its hydrolysis of both N alpha-acetylglycyl-L-lysine-methyl ester-acetate and H-D-Glu-Gly-Arg-pNA (S-2227), bilokinase showed similar Km values to those of urokinase; however, they were quite distinct from those of plasmin. It was concluded therefore that bilokinase is a plasminogen activator with enzymatic properties which are quite similar to those of the urinary plasminogen activator urokinase. The origin of bilokinase and its relation to liver function are now under investigation.