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Hot Biological Catalysis: Isothermal Titration Calorimetry to Characterize Enzymatic Reactions
Published on: April 4, 2014
A mechanistic model for butyrylcholinesterase.
Biochimica Et Biophysica Acta
|March 16, 1979
Summary
Horse serum butyrylcholinesterase exhibits substrate activation during deacylation. Its catalytic activity persists across various forms, including monomeric and aggregated states, despite a tetrameric native structure.
Area of Science:
- Biochemistry
- Enzymology
Background:
- Butyrylcholinesterase (BChE) is a crucial enzyme found in horse serum.
- Understanding its mechanism of action is vital for biochemical and pharmacological studies.
Purpose of the Study:
- To propose a plausible mechanism of action for horse serum butyrylcholinesterase.
- To investigate the role of substrate concentration on enzyme kinetics and subunit interactions.
Main Methods:
- Kinetic analysis of enzyme acylation and deacylation rates.
- Enzyme labeling studies using [32P]diisopropylfluorophosphate.
- Inhibitor binding studies with N-methylacridine.
Main Results:
- Substrate activation occurs at the deacylation step.
- Acylation rate constants are significantly higher than deacylation rate constants at low substrate concentrations.
- Rate constants become comparable at higher substrate concentrations.
- No inter-subunit interactions were observed in inhibitor binding or catalysis.
- Each subunit possesses one esteratic and one anionic site.
- Catalytic activity is retained in monomeric, aggregated, and dissociated states, not just the native tetrameric form.
Conclusions:
- A detailed mechanism for horse serum BChE action is proposed, highlighting substrate-dependent kinetics.
- The enzyme's active sites and subunit structure were characterized.
- The enzyme's functional flexibility across different quaternary structures was demonstrated.
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