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Light-dependent reduction of dehydroascorbate by ruptured pea chloroplasts
1Botany Department, La Trobe University, Bundoora, Victoria 3083, Australia.
Plant Physiology
|June 1, 1981
Summary
Pea shoot glutathione dehydrogenase was purified and characterized. Light-dependent reactions in chloroplasts involve glutathione reductase and glutathione dehydrogenase, with GSSG reduction being rate-limiting.
Area of Science:
- Biochemistry
- Plant Physiology
- Enzymology
Background:
- Glutathione dehydrogenase (EC 1.8.5.1) plays a role in cellular redox balance.
- Understanding its function in plants, particularly within chloroplasts, is crucial for plant physiology.
Purpose of the Study:
- To partially purify and characterize glutathione dehydrogenase from pea shoots.
- To investigate the enzyme's activity within isolated chloroplasts under light conditions.
Main Methods:
- Partial purification of glutathione dehydrogenase from pea shoots.
- Enzyme kinetics studies, including pH optimum and K(m) determination.
- Assay of enzyme activity in isolated, illuminated pea chloroplasts.
Main Results:
- The enzyme exhibited a pH optimum of 7.6 with specific K(m) values for reduced glutathione (GSH) and dehydroascorbate.
- Iodoacetate and copper sulfate inhibited enzyme activity, while zinc chloride and sodium azide showed minimal inhibition.
- Illuminated chloroplasts demonstrated (dehydroascorbate plus glutathione)-dependent O(2) evolution, linked to dehydroascorbate reduction.
- Zinc chloride inhibited O(2) evolution but not ascorbate formation.
- Light-dependent reduction of oxidized glutathione (GSSG) via glutathione reductase was identified as the rate-limiting step.
Conclusions:
- Glutathione dehydrogenase activity is present in pea shoot chloroplasts.
- A light-dependent reaction sequence involving glutathione reductase and glutathione dehydrogenase facilitates ascorbate formation.
- The reduction of GSSG is the rate-limiting factor in this pathway at physiological GSH concentrations.