PHYSICOCHEMICAL CHARACTERIZATION OF THE MAIN FACTORS AFFECTING THE MODE OF ACTION OF LIVER ALCOHOL-DEHYDROGENASE IMMOBILIZED ON NYLON TUBING

Alcohol dehydrogenase (ADH) from horse liver (EC 1.1.1.1), cross-linked through the bifunctional reactive glutaraldehyde, onto nylon tubing was immobilized (35-mu-g cm-2 internal surface of nylon tubing). ADH inactivation kinetics of the immobilized enzyme are of first order (t1/2 = 84.3 h, k = 8.2 x 10(-3) h-1 at 5-degrees-C; t1/2 = 2.6 h, k = 0.26 h-1 at 50-degrees-C). The activity versus pH profile points to a smaller effect of pH on the activity of the enzyme, which is the case of ADH in solution, explicable on the basis of limitations to proton diffusion towards/from the support. A limiting effect to free external diffusion of the substrate (products) towards/from the support was observed; this effect seems to determine the effective kinetic behaviour of immobilized ADH.