Kinetic studies on soluble and insoluble urokinases

A water-insoluble urokinase (ins-UK) was prepared by covalent coupling to an electrostatically neutral polyacrylamide derivative. The esteratic activity retained by the bound enzyme is about 70 percent of that of the soluble urokinase (UK). Comparative kinetic studies of these two forms of the enzyme were undertaken on lysine esters: N-alpha-acetyl-L-lysine-methyl ester (ALEe) and N-alpha acetylglycyl-L-lysine methyl ester (AGLMe). It was first observed that these substrates both exhibit a marked inhibitory effect toward soluble UK, whereas this phenomenon was less manifest with the insoluble form of the enzyme. Michaelis constants and maximal velocities measured at 33 degrees C, for UK and ins-UK, were identical when ALMe was used, but slightly different with AGLMe. Determination of initial velocities, at a series of pH values shows only minimal differences in the behavior of the soluble enzyme with respect to that of the insoluble form. However, over a range of temperatures, differing Km values for these two enzyme forms were obtained using AGLMe as the substrate. These last results suggest possible interactions between the substrate and the insoluble carrier of the enzyme.