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Light-driven Enzymatic Decarboxylation
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Reverse Ordered Sequential Mechanism for Lactoperoxidase with Inhibition by Hydrogen Peroxide
Kellye Cupp-Sutton1, Michael T Ashby1
1Department of Chemistry and Biochemistry, University of Oklahoma, Norman, OK 73019, USA.
Antioxidants (Basel, Switzerland)
|November 27, 2021
Summary
Lactoperoxidase (LPO) enzyme activity is better explained by a reversed substrate binding order. This new mechanism clarifies enzyme kinetics and inhibition, offering insights into its antimicrobial function.
Area of Science:
- Biochemistry
- Enzymology
- Antimicrobial mechanisms
Background:
- Lactoperoxidase (LPO) is a key enzyme in mucosal secretions, producing antimicrobial hypothiocyanite (OSCN-) via thiocyanate (SCN-) oxidation by hydrogen peroxide (H2O2).
- The established halogen cycle mechanism for LPO catalysis does not account for observed biphasic kinetics or H2O2 inhibition under certain conditions.
Purpose of the Study:
- To propose and investigate an alternative catalytic mechanism for Lactoperoxidase.
- To explain the biphasic kinetics and substrate inhibition phenomena observed in LPO activity.
Main Methods:
- Kinetic analysis of Lactoperoxidase activity.
- Proposing and evaluating an ordered sequential mechanism with reversed substrate binding order.
Main Results:
- The accepted halogen cycle mechanism fails to explain specific kinetic behaviors of LPO.
- An alternative ordered sequential mechanism, with initial binding of SCN- followed by H2O2, better accounts for observed kinetics and inhibition patterns.
- The substrate binding order in the halogen cycle is shown to be inhibitory.
Conclusions:
- A revised understanding of the Lactoperoxidase catalytic mechanism is proposed, involving a reversed substrate binding sequence.
- This new model provides a more comprehensive explanation for LPO enzyme kinetics and its role in antimicrobial defense.
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