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Related Experiment Videos

Interfacial catalysis by phospholipase A2: substrate specificity in vesicles.

F Ghomashchi1, B Z Yu, O Berg

  • 1Department of Chemistry, University of Washington, Seattle 98195.

Biochemistry
|July 23, 1991
PubMed
Summary
This summary is machine-generated.

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Phospholipase A2 (PLA2) enzyme activity is enhanced on mixed lipid vesicles, improving substrate specificity studies. A new double-radiolabel method accurately measures PLA2 substrate preferences without binding affinity issues.

Area of Science:

  • Biochemistry
  • Enzyme Kinetics
  • Lipid Metabolism

Background:

  • Interfacial binding of phospholipase A2 (PLA2) significantly impacts its catalytic kinetics.
  • Interpreting substrate specificity data is challenging due to the contribution of binding to overall turnover.
  • PLA2 binding to zwitterionic phospholipid vesicles is generally poor, complicating kinetic analysis.

Purpose of the Study:

  • To investigate the action of PLA2 on mixed lipid vesicles containing zwitterionic and anionic phospholipids.
  • To understand the mechanism of hydrolysis and enzyme-substrate interactions at the interface.
  • To develop a novel method for accurately determining PLA2 substrate specificity.

Main Methods:

  • Studied PLA2 hydrolysis on mixed phosphatidylcholine (PC) and phosphatidic acid (PA) vesicles.

Related Experiment Videos

  • Utilized a double-radiolabel approach with 3H- and 14C-labeled phospholipids for specificity determination.
  • Analyzed fatty acid products to calculate substrate specificity constants (kcat/KMS) in scooting mode hydrolysis.

    • Main Results:

    • PLA2 hydrolysis on mixed PC/PA vesicles occurred in a 'scooting mode' with enhanced enzyme binding.
    • Hydrolysis rate of PC in mixed vesicles was increased over 50-fold compared to pure PC vesicles.
    • PLA2s showed no discrimination between PC and phosphatidylethanolamine, or saturated/unsaturated acyl chains; pig PLA2 preferred anionic phospholipids slightly.

    Conclusions:

    • The presence of anionic phospholipids significantly enhances PLA2 binding and catalytic activity on mixed vesicles.
    • The 'scooting mode' hydrolysis is not limited to pure anionic vesicles but occurs with zwitterionic lipids containing critical anionic amounts.
    • The developed double-radiolabel protocol provides accurate PLA2 substrate specificity measurements, independent of differential binding affinities.