Temperature and pH effects with immobilized electric eel acetylcholinesterase

Area of Science:

• Biochemistry
• Enzyme kinetics
• Biomaterials

Background:

• Immobilized enzymes offer advantages in stability and reusability.
• Acetylcholinesterase (AChE) is crucial for neurotransmission and is a target for various inhibitors.
• Understanding the kinetics of immobilized enzymes is vital for optimizing their applications.

Purpose of the Study:

• To investigate the kinetic properties of immobilized acetylcholinesterase under varying substrate concentrations and temperatures.
• To compare the behavior of AChE immobilized in polyacrylamide gel versus nylon tubing.
• To elucidate the influence of local pH changes on the activity of immobilized AChE.

Main Methods:

• Kinetic studies of immobilized acetylcholinesterase (AChE) using two forms: polyacrylamide gel slices and nylon tubing.
• Enzyme rate measurements at low and high substrate concentrations relative to the Michaelis constant.
• Temperature range: 16-40°C.
• Analysis of Arrhenius plots and pH-dependent activity.

Main Results:

• Low activation energies (1.7-2.7 kcal mol-1) at low substrate concentrations indicate diffusion control.
• Non-linear Arrhenius plots and higher activation energies at high substrate concentrations suggest reduced diffusion control.
• Enzyme-polyacrylamide slices showed a continuous rate increase with pH, unlike the bell-shaped curve for free enzyme.
• Theoretical analysis points to local pH decrease due to hydrolysis acid as the cause for altered pH-dependent activity.

Conclusions:

• Immobilization significantly impacts acetylcholinesterase kinetics, particularly concerning substrate diffusion and local microenvironment effects.
• The observed pH-dependent activity in immobilized AChE is influenced by the local pH changes resulting from substrate hydrolysis.
• These findings are crucial for designing and implementing effective immobilized enzyme systems in various applications.