Immobilized electric eel acetylcholinesterasemii. II. Flow kinetics of acetylcholinesterase chemically attached to nylon tubing

Flow kinetics of yeast alcohol dehydrogenase attached to nylon tubing

Yeast alcohol dehydrogenase (alcohol:NAD+ oxidoreductase, EC 1.1.1.1) was attached covalently to the inner surface of nylon tubing, and the immobilized enzyme retained its activity over a period of months. A study was made of the flow kinetics for the reaction between ethanol and NAD. With the ethanol held at saturating concentrations there was partial diffusion control, the extent decreasing with increasing flow rate and increasing NAD concentration. With the NAD at saturating concentrations there was no appreciable diffusion control. The apparent Michaelis constants varied with flow rate vf, being linear in vf-1/3, and extrapolation to infinite flow rate (vf-1/3 = 0) gave the intrinsic Michaelis constants. The inhibition by products was also studied. The results for both NADH and acetaldehyde showed mixed competitive and non-competitive inhibition, with a preponderance of the former. Acetaldehyde is the stronger inhibitor, and this is consistent with the lack of dissusion control with variable ethanol. Inhibition by acetaldehyde is not affected by flow rate, but inhibition by NADH is affected, presumably because of the greater degree of diffusion control with variable NAD.

Temperature and pH effects on immobilized lactate dehydrogenase kinetics

Rabbit muscle lactate dehydrogenase (EC 1.1.1.27) was attached covalently to the inner surface of nylon tubing, and kinetic measurements made. The results were interpreted on the basis of the Kobayashi-Laidler treatment of immobilized enzymes in flow systems, various tests being applied to determine the degree of diffusion control. It was established in various ways that the degree of diffusion control increases with (a) decrease in flow rate, (b) decrease in substrate concentration, and (c) decrease in temperature. A number of quantitative relationships, predicted by the theory, were obeyed by the results, for example: (a) Km(app) varies linearly with vf-1/3, where vf is the flow rate, (b) the logarithm of the product concentration at the exit varies linearly with the logarithm of the flow rate, and (c) absolute calculations of product concentrations are in reasonable agreement with experiment. A value of 5 kcal . mol-1 is estimated for the activation energy of the diffusion processes, and of 1 kcal . mol-1 for the chemical processes. When the pH is varied the rates pass through a flat maximum, the pH dependence being less than with the free enzyme.

Multilayer immobilized-enzyme filter reactors: urease bound to nylon fabric filters

Urease was bound to commercially available nonwoven nylon fabric filters. Multilayer immobilized-enzyme filter reactors were constructed by packing varying numbers of urease-nylon filters in a column. Owing to the relatively open structure and high mechanical strength of the filter fabric, compaction and pressure drop effects were minimal. The reactors could be operated in a wide range of substrate concentrations and flow rates under conditions where mass-transfer limitations could be neglected. The kinetic behavior of the immobilized-enzyme filter reactors could be described by a linear form of the integrated Michaelis-Menten equation using a model based on the sequential action of the enzyme filters.

Temperature and pH effects with immobilized electric eel acetylcholinesterase

Kinetic studies were made with 2 forms of immobilized acetylcholinesterase: enzyme trapped in polyacrylamide gel which was cut into slices; and enzyme attached to the inner surface of nylon tubing. Rates were measured at substrate concentrations which were low and high with reference to the Michaelis constant, and over the temperature range 16-40 degrees C. Low activation energies (1.7-2.7 kcal mol-1) were obtained at low substrate concentrations, indicating diffusion control. At high substrate concentrations the Arrhenius plots were non-linear and the activation energies substantially higher, and there is less diffusion control. With enzyme-polyacrylamide slices, there was a continuous increase in rate with increasing pH, in contrast to the bell-shaped behavior with free enzyme. A theoretical treatment suggests that this is due to the lowering of local pH as a result of the acid released in the hydrolysis.

Hydrolysis of D-galactosides in an open tubular lactase reactor

Lactase (beta-galactosidase) was attached to the inner surface of nylon tubing. Tubes of various lengths were used to bring about the hydrolysis of o-nitrophenyl-beta-D-galactoside and of lactose in skim milk. The results with the former substrate were analyzed in the light of a theoretical treatment of Kobayashi and Laidler (Biotechnol. Bioeng., 16, 99, 1974), with the conclusion that the reaction is intermediate between diffusion-free and completely diffusion-controlled behavior. The results with skim milk show that with a single 46 m tube and continuous circulation, 90% of the lactose is removed within 20 hr. A battery of ten such tubes, with single passage, at a flow rate of 2 cm/sec, would remove more than 99% of the lactose in less than 40 min.