Cholinesterase: substrate inhibition and substrate activation.

Area of Science:

• Biochemistry
• Enzyme kinetics

Background:

• Acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) are crucial enzymes involved in neurotransmission and detoxification.
• Understanding their kinetic behavior, particularly substrate concentration-dependent activity, is vital for pharmacology and toxicology.

Purpose of the Study:

• To analyze the relationship between enzyme activity and substrate concentrations (pS-curves) for AChE and BChE.
• To differentiate between true substrate inhibition and apparent substrate effects using kinetic parameters.
• To refine the terminology for substrate-induced changes in enzyme activity.

Main Methods:

• Enzyme activity assays were performed across a range of substrate concentrations for AChE and BChE.
• Kinetic constants (Km, Kss, Vm, n, b) were calculated using established models (Michaelis-Menten, Haldane, Hill, Webb).
• pS-curves were generated to visualize the relationship between substrate concentration and reaction velocity.

Main Results:

• Analysis revealed distinct patterns in pS-curves for different substrates and enzymes.
• Calculated kinetic constants provided quantitative measures to assess substrate interactions.
• Substrates exhibiting bell-shaped pS-curves were identified as exhibiting true substrate inhibition.

Conclusions:

• The study recommends using 'substrate inhibition' exclusively for enzymes showing bell-shaped pS-curves.
• Apparent substrate inhibition or activation should be associated with calculated kinetic constant values.
• This refined terminology enhances clarity in describing enzyme kinetics and substrate interactions.