Intact spinach chloroplasts scavenge hydrogen peroxide with a peroxidase that uses a photoreductant as the electron donor, but the activity of ruptured chloroplasts is very low [Nakano and Asada (1980) Plant & Cell Physiol. 21: 1295]. Ruptured spinach chloroplasts recovered their ability to photoreduce hydrogen peroxide with the concomitant evolution of oxygen after the addition of glutathione and dehydroascorbate (DHA). In ruptured chloroplasts, DHA was photoreduced to ascorbate and oxygen was evolved in the process in the presence of glutathione. DHA reductase (EC 1.8.5.1) and a peroxidase whose electron donor is specific to L-ascorbate are localized in chloroplast stroma. These observations confirm that the electron donor for the scavenging of hydrogen peroxide in chloroplasts is L-ascorbate and that the L-ascorbate is regenerated from DHA by the system: photosystem I-*ferredoxin-*NADP^>glutathione. A preliminary characterization of the chloroplast peroxidase is given.

Hydrogen Peroxide is Scavenged by Ascorbate-specific Peroxidase in Spinach Chloroplasts

When hemolyzates from erythrocytes of selenium-deficient rats were incubated in vitro in the presence of ascorbate or H(2)O(2), added glutathione failed to protect the hemoglobin from oxidative damage. This occurred because the erythrocytes were practically devoid of glutathione-peroxidase activity. Extensively purified preparations of glutathione peroxidase contained a large part of the (75)Se of erythrocytes labeled in vivo. Many of the nutritional effects of selenium can be explained by its role in glutathione peroxidase.

https://science.sciencemag.org/content/sci/179/4073/588.full.pdf

Selenium: Biochemical Role as a Component of Glutathione Peroxidase

Publisher Summary This chapter focuses on the diversity of glutathione peroxidases Selenium was identified as a toxic factor for grazing animals in the first half of the twentieth century and since then has been considered hazardous Only long after the identification of the first selenoenzymes in bacteria and mammals was a Recommended Dietary Allowance gradually established In fact, the putative biological roles of the selenoenzymes, particularly those of the glutathione peroxidases (GPX), proved instrumental in the understanding of selenium deficiency syndromes in livestock and humans, although the emerging complexity of selenium enzymology still precludes definitive conclusions The selenium-dependent peroxidases have long been considered a late achievement of evolution, as they were only detected in vertebrates This view now has to be revised Whether the common ancester of the GPX superfamily was a selenoprotein or a cysteine-containing homolog cannot be deduced from the available sequences The only prokaryotic member of the superfamily detected so far, a cobalamine-binding protein of Escherichia coli , does not contain selenocysteine, and despite ongoing efforts, functionally active glutathione peroxidases have not yet been found in prokaryotes

Diversity of glutathione peroxidases.

Protective action of phospholipid hydroperoxide glutathione peroxidase against membrane-damaging lipid peroxidation. In situ reduction of phospholipid and cholesterol hydroperoxides.

Ascorbate peroxidase, a key enzyme for the scavenging of hydrogen peroxide in chloroplasts, was found in a thylakoid-bound form in spinach chloroplasts at comparable activity to that in the stroma. The activity of peroxidase was detectable in the thylakoids only when prepared by an ascorbate-containing medium, and enriched in the stroma thylakoids. The thylakoid enzyme was not released from the membranes by either 2 mM EDTA, 1 M KC1, 2 M NaBr or 2 M NaSCN, but was solubilized by detergents. Enzymatic properties of the thylakoid-bound ascorbate peroxidase were very similar to those of the stromal ascorbate peroxidase. Thylakoid-bound ascorbate peroxidase could scavenge the hydrogen peroxide either added or photoproduced by the thylakoids. No photoreductio n of hydrogen peroxide was observed, however, in the thylakoids whose ascorbate peroxidase was inhibited by KCN and thiol reagents or inactivated by the treatment with ascorbate-depletion. The primary oxidation product of ascorbate in a reaction of ascorbate peroxidase, monodehydroascorbate (MDA) radical, was photoreduced in the thylakoids, as detected by the quenching of chlorophyll fluorescence, disappearance of EPR signals of the MDA radicals and the MDA radical-induced oxygen evolution. Thus, ascorbate is photoregenerated in the thylakoids from the MDA radicals produced in a reaction of ascorbate peroxidase for the scavenging of hydrogen peroxide.

Thylakoid-Bound Ascorbate Peroxidase in Spinach Chloroplasts and Photoreduction of Its Primary Oxidation Product Monodehydroascorbate Radicals in Thylakoids

http://www.jbc.org/content/245/14/3632.full.pdf

Clive Little

Papers

Properties and regulation of glutathione peroxidase.

Steroid hydroperoxides as substrates for glutathione peroxidase.

Inhibition of glutathione peroxidase by coenzyme A