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Plant Physiology 67:1239-1244 (1981)
© 1981 American Society of Plant Biologists

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Light-Dependent Reduction of Dehydroascorbate by Ruptured Pea Chloroplasts 1

Peter P. Jablonski2 and John W. Anderson

Botany Department, La Trobe University, Bundoora, Victoria 3083, Australia

Glutathione dehydrogenase (EC 1.8.5.1) was partially purified from pea shoots. The pH optimum was 7.6. The Km values for GSH and dehydroascorbate were 4.4 and 0.44 millimolar, respectively. The enzyme was inhibited by iodoacetate and CuSO4 but not significantly by ZnCl2 or NaN3. Part of the total enzyme activity was associated with isolated chloroplasts.

Illuminated ruptured chloroplasts, in the presence of 50 micromolar NADP(H) and substrate concentrations of GSH or GSSG, catalyzed (dehydroascorbate plus glutathione)-dependent O2 evolution with the concomitant reduction of dehydroascorbate to ascorbate. Oxidation of ascorbate by ascorbate oxidase activity associated with the chloroplasts was relatively insignificant. ZnCl2 inhibited (dehydroascorbate plus glutathione)-dependent O2 evolution but not ascorbate formation. The reaction was attributed to light-dependent reduction of GSSG (involving glutathione reductase) coupled to the reduction of dehydroascorbate (involving glutathione dehydrogenase). Light-dependent reduction of GSSG appears to be the rate-limiting step in this reaction sequence at physiological concentrations of GSH.

2 Holder of a La Trobe University Postgraduate Scholarship.

1 This work was supported by a grant from the Australian Research Grants Committee.




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 Plant Cell PhysiolHome page
T. Shimaoka, A. Yokota, and C. Miyake
Purification and Characterization of Chloroplast Dehydroascorbate Reductase from Spinach Leaves
Plant Cell Physiol., October 1, 2000; 41(10): 1110 - 1118.
[Abstract] [Full Text] [PDF]


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Copyright © 1981 by the American Society of Plant Biologists