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Human plasma dopamine beta-hydroxylase. Purification and properties.

R P Frigon, R A Stone

    The Journal of Biological Chemistry
    |October 10, 1978
    PubMed
    Summary

    Researchers purified dopamine beta-hydroxylase from human plasma, identifying a major tetrameric form and a minor dimeric form. Both enzyme variants are glycoproteins and show no immunochemical differences, suggesting related structures in plasma.

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    Area of Science:

    • Biochemistry
    • Enzymology
    • Human Physiology

    Background:

    • Dopamine beta-hydroxylase (DBH) is a key enzyme in catecholamine biosynthesis.
    • Understanding DBH structure and forms in human plasma is crucial for its physiological role.
    • Previous studies have indicated the presence of DBH in plasma, but its characterization remains incomplete.

    Purpose of the Study:

    • To isolate and purify dopamine beta-hydroxylase from normal human plasma.
    • To characterize the different molecular forms of DBH present in plasma.
    • To compare the biochemical and immunochemical properties of these DBH forms.

    Main Methods:

    • Enzyme purification using affinity chromatography (immobilized concanavalin A, hydrophobic interaction chromatography).
    • Molecular weight determination (gel filtration, SDS-PAGE).
    • Kinetic analysis, Stokes radii, and sedimentation coefficient (S20,W) measurements.
    • Immunotitration using rabbit antiserum against purified DBH.

    Main Results:

    • Two forms of dopamine beta-hydroxylase were isolated from human plasma: a major 300,000-dalton tetramer and a minor 20% dimeric form.
    • The tetrameric form consists of 72,000-dalton subunits linked by disulfide bonds.
    • Both DBH forms are glycoproteins, interacting with concanavalin A and exhibiting hydrophobic properties.
    • Kinetic analysis and biophysical characterization revealed differences in Stokes radii and S20,W between the tetramer and dimer.
    • Immunotitration showed no immunochemical differences between the two plasma DBH forms.

    Conclusions:

    • Human plasma contains at least two distinct molecular forms of dopamine beta-hydroxylase.
    • These forms, a tetramer and a dimer, share structural similarities as indicated by immunochemical analysis.
    • The purification and characterization of plasma DBH provide insights into its potential roles and regulation in vivo.

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