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Indirect-acting cholinergic agonists work by interacting with an enzyme called acetylcholinesterase (AChE) in the synaptic cleft. They can be reversible or irreversible inhibitors and have different effects on the enzyme.
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Indirect-acting cholinergic agonists are agents that interact with the acetylcholinesterase enzyme in the synaptic cleft, preventing the breakdown of acetylcholine into choline and acetate. Consequently, the concentration of acetylcholine in the synaptic cleft increases. These agonists can be classified into reversible and irreversible inhibitors based on their duration of action.
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Related Experiment Video

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Cholinesterase: substrate inhibition and substrate activation.

Elsa Reiner1, Vera Simeon-Rudolf1

  • 1Institute for Medical Research and Occupational Health, Ksaverska cesta 2, POBox 291, HR-10001, Zagreb, Croatia, Croatia.

Pflugers Archiv : European Journal of Physiology
|December 24, 2016
PubMed
Summary

This study analyzes enzyme kinetics for acetylcholinesterase and butyrylcholinesterase, examining substrate concentration effects. It proposes distinct definitions for substrate inhibition and activation based on enzyme activity curves and calculated constants.

Keywords:
Key words acetylcholinesteraseapparent substrate inhibition and activation.butyrylcholinesterasecatalytic constantssubstrate inhibition and activation

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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.