Urokinase (UK, EC 3.4.99.26), a plasminogen activator, has been immobilized by the various methods using various kinds of the matrix. The problems was due to short biological half life when injected.
For the dual purpose of UK immobilization in this study, we tried to prepare the immobilized UK on water soluble nontoxic biopolymer, dextran. When injected, this is for improve short biological half life $\underline{in}$ $\underline{vivo}$ primarily and also for the expansion of plasma.
Five mg UK was coupled to 100 mg dextran (MW $7 x 10^4$) after the polysaccharide was activated by the cyanogen bromide method. The resulting soluble dextran-urokinase conjugate was purified by gel permeation chromatography using Sephadex G-200. After coupling, the conjugate had 15% of the fibrinolytic activity of the native enzyme. The water soluble dextran-urokinase conjugate was characterized with regard to pH and temperature dependences, storage and thermal stabilities.
The resulting conjugate showed greater resistance than the native enzyme to heat inactivation, autolysis, pH effect, and was also more resistant to the inhibition effect of plasma. Treatment with dextranase, the molecular size of conjugate was decreased and the stability of the conjugate molecule against plasma was decreased slightly. On the polyacrylamide gel electrophoresis, one molecule of the conjugate appeared to have many UK and dextran molecules linked together. Intermolecular cross-linking of the enzyme molecules by polysaccharides is considered to be responsible for stabilization of the tertiary structure of the enzyme molecule in the conjugate.
When dextran-urokinase conjugate (approx. 500 CTA units) was administered to rats (av. wt. approx. 220 g) via their femoral vein cannula with polyethylene tube, dextran-urokinase conjugate showed much higher resistance than native urokinase (approx. 2,700 CTA units) and urokinase/dextran mixture (approx. 3,000 CTA units) against the inhibition effects of plasma.
