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Human plasma platelet-activating factor acetylhydrolase. Purification and properties.

D M Stafforini, S M Prescott, T M McIntyre

    The Journal of Biological Chemistry
    |March 25, 1987
    PubMed
    Summary

    Researchers purified plasma PAF-acetylhydrolase, an enzyme that inactivates platelet-activating factor (PAF). This enzyme plays a key role in regulating PAF

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    Area of Science:

    • Biochemistry
    • Lipid Metabolism
    • Enzymology

    Background:

    • Platelet-activating factor (PAF) is a potent bioactive phospholipid involved in inflammation and hypotension.
    • PAF's biological activity is dependent on its acetyl group at the sn-2 position.
    • A specific acetylhydrolase in plasma and tissues inactivates PAF by removing this acetyl group.

    Purpose of the Study:

    • To purify and characterize the plasma enzyme responsible for PAF inactivation.
    • To understand the enzymatic properties and substrate specificity of PAF-acetylhydrolase.

    Main Methods:

    • Purification of plasma PAF-acetylhydrolase using a rapid assay involving reversed-phase columns.
    • Ultracentrifugation to determine substrate association with lipoproteins.
    • Enzymatic assays to determine kinetic parameters (Km, Vmax) and substrate preferences.

    Main Results:

    • The enzyme was purified 25,000-fold from plasma, with 70% of activity associated with low-density lipoproteins.
    • Purified PAF-acetylhydrolase has a molecular weight of 43,000, does not require calcium, and prefers micellar substrates.
    • Apparent Km is 13.7 microM and Vmax is 568 mumol/h/mg for micellar PAF; it shows preference for the sn-2 acetyl group.

    Conclusions:

    • A specific and potent PAF-acetylhydrolase has been purified from human plasma.
    • The enzyme's properties suggest a significant role in regulating PAF levels and biological effects.
    • Further characterization supports its classification as a specific PAF-inactivating enzyme.

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