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The competition between methyl viologen and monodehydroascorbate radical as electron acceptors in spinach thylakoids and intact chloroplasts.
- Source :
-
Free radical research [Free Radic Res] 2000 Sep; Vol. 33 (3), pp. 217-27. - Publication Year :
- 2000
-
Abstract
- In spinach thylakoids prepared from intact chloroplasts by shocking in the presence of ascorbate to preserve the operation of ascorbate peroxidase, the rate of oxygen uptake with methyl viologen as acceptor decreased in response to the addition of H2O2. Such a decrease was not observed in the presence of KCN or when the thylakoids lost ascorbate peroxidase activity. Illumination of intact chloroplasts in the presence of H2O2 and methyl viologen showed an initial rate of oxygen exchange, which is intermediate between the initial rate of oxygen evolution in the presence of H2O2 alone and steady-state oxygen uptake in the presence of methyl viologen. The data showed that monodehydroascorbate radical generated in ascorbate peroxidase reaction could compete with methyl viologen for electrons supplied by the electron transport chain in both thylakoids and intact chloroplasts. During the illumination of intact chloroplasts the rate of oxygen uptake increased. The presence of nigericin swiftly led to steady-state oxygen uptake, and to a clear-cut 1:1 relationship between the electron transport rate estimated from fluorescence assay and the electron transport rate determined from oxygen uptake, taking the stoichiometry 1 O2:4 e. The increase in oxygen uptake was attributed to the cessation of monodehydroascorbate radical generation brought about by consumption of intrachloroplast ascorbate in the peroxidase reactions, and the effects of nigericin were explained by acceleration of such consumption. The competition between methyl viologen and monodehydroascorbate radical in the intact chloroplasts was estimated under various conditions.
- Subjects :
- Ascorbate Peroxidases
Ascorbic Acid metabolism
Binding, Competitive
Electron Transport
Free Radicals
Hydrogen Peroxide metabolism
Hydrogen Peroxide pharmacology
NADP metabolism
Oxidation-Reduction
Oxygen metabolism
Peroxidases metabolism
Potassium Cyanide pharmacology
Thylakoids
Chloroplasts metabolism
Dehydroascorbic Acid analogs & derivatives
Dehydroascorbic Acid metabolism
Paraquat metabolism
Spinacia oleracea ultrastructure
Subjects
Details
- Language :
- English
- ISSN :
- 1071-5762
- Volume :
- 33
- Issue :
- 3
- Database :
- MEDLINE
- Journal :
- Free radical research
- Publication Type :
- Academic Journal
- Accession number :
- 10993476
- Full Text :
- https://doi.org/10.1080/10715760000301391