Immobilization of urea cycle enzymes. II. Characterization of immobilized argininosuccinate synthetase.

Argininosuccinate synthetase (EC 6.3.4.5) was immobilized on CNBr-activated Sepharose 4B. Properties of the immobilized enzyme are described and compared with those of the native enzyme. The immobilized enzyme was much more stable than the native enzyme at 37 degrees C. It was further stabilized in the presence of the assay reagents. The optimum pH of the immobilized enzyme shifted towards alkalinity (approximately 0.5 unit). The apparent Michaelis constants measured for the immobilized enzyme were not greatly different from those measured for the native enzyme. Urea formation from citrulline was confirmed in a continuous column reactor by the coimmobilized argininosuccinate synthetase, argininosuccinate lyase (EC 4.3.2.1), and arginase (EC 3.5.3.1).