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Ascorbate free-radical reduction by glyoxysomal membranes.

M L Bowditch1, R P Donaldson

  • 1Department of Biological Sciences, George Washington University, Washington, DC 20052.

Plant Physiology
|October 1, 1990
PubMed
Summary

Castor bean glyoxysomal membranes possess an NADH dehydrogenase that reduces ascorbate free-radical. This enzyme links glyoxysomal metabolism to cellular activities by regenerating NAD(+).

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Area of Science:

  • Plant Biochemistry
  • Cellular Respiration
  • Membrane Transport

Background:

  • Glyoxysomes are crucial for fatty acid metabolism in plants.
  • NADH dehydrogenase activity in glyoxysomal membranes is not fully understood.
  • The role of ascorbate in glyoxysomal redox balance requires investigation.

Purpose of the Study:

  • To identify and characterize the NADH dehydrogenase in castor bean glyoxysomal membranes.
  • To determine if ascorbate free-radical can serve as a substrate for this enzyme.
  • To elucidate the function of NADH:ascorbate free-radical reductase in glyoxysomal redox homeostasis.

Main Methods:

  • Isolation and lysis of glyoxysomes from germinating castor bean endosperm.
  • Enzyme assays for NADH:ascorbate free-radical reductase, NADH:ferricyanide reductase, and NADH:cytochrome c reductase.
  • Enzyme sensitivity assays (trypsin, Triton X-100) and subcellular fractionation.
  • Rate-zonal centrifugation of solubilized membrane proteins.

Main Results:

  • A membrane-associated NADH dehydrogenase utilizing ascorbate free-radical was identified.
  • The enzyme's activity supported intraglyoxysomal NAD(+) demand.
  • NADH:ascorbate free-radical reductase showed distinct properties from NADH:cytochrome c reductase, being insensitive to trypsin and detergent.
  • Comigration studies suggested a common component for ascorbate and ferricyanide reduction.

Conclusions:

  • The glyoxysomal membrane contains an NADH dehydrogenase that reduces ascorbate free-radical.
  • This redox system may link glyoxysomal metabolism to broader cellular activities.
  • Ascorbate reduction by the glyoxysomal membrane redox system could play a role in cellular signaling or antioxidant defense.

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