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Aspergillus niger sulfhydryl oxidase.

R S de la Motte1, F W Wagner

  • 1Department of Biochemistry, University of Nebraska, Lincoln 68583-0718.

Biochemistry
|November 17, 1987
PubMed
Summary
This summary is machine-generated.

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This study isolated a sulfhydryl oxidase enzyme from Aspergillus niger, revealing its glycoprotein nature and ability to oxidize glutathione and other thiols, crucial for protein thiol group oxidation.

Area of Science:

  • Biochemistry
  • Enzymology

Background:

  • Sulfhydryl oxidase enzymes play a role in cellular redox homeostasis.
  • Understanding the properties of these enzymes is essential for various biochemical applications.

Purpose of the Study:

  • To isolate and characterize a sulfhydryl oxidase from Aspergillus niger.
  • To determine its enzymatic activity, substrate specificity, and kinetic properties.

Main Methods:

  • Enzyme isolation using a three-step procedure.
  • Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) for molecular weight determination.
  • Sedimentation equilibrium experiments for native molecular weight analysis.
  • Enzymatic assays to determine kinetic parameters (Km, pH optimum) and substrate specificity.

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  • Spectroscopic analysis (UV-visible) for flavoprotein characterization.

    • Main Results:

    • Isolated a sulfhydryl oxidase as a glycoprotein (20.3% neutral hexose, 1.9% aminohexose) with a subunit molecular weight of 53,000 Da and native molecular weight of 106,000 Da.
    • The enzyme efficiently catalyzes the oxidation of reduced glutathione (GSH) to its disulfide form, with a 2:1 ratio of GSH consumed to H2O2 produced.
    • Optimum pH for GSH oxidation is 5.5 at 25°C, with a Michaelis constant (Km) of 0.3 mM for GSH. Other thiols showed higher Km values.
    • Demonstrated enhancement of ribonuclease A reactivation, indicating oxidation of protein-associated thiol groups.
    • UV-visible spectrum is characteristic of flavoproteins.

    Conclusions:

    • The isolated Aspergillus niger sulfhydryl oxidase is a flavoprotein glycoprotein with specific activity towards reduced glutathione.
    • The enzyme's ability to oxidize protein-associated thiols suggests a role in protein folding and disulfide bond formation.
    • Kinetic data provides insights into substrate preferences and catalytic efficiency.