Photochemical Oxidation and Reduction of Plastoquinone sensitized by Isolated Chlorophylls

Okayama, Shigeki; Chiba, Yasutane

doi:10.1038/205172a0

Cited by 4 publications

(2 citation statements)

References 11 publications

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“…Under normal conditions, chlorophyll* transfers electrons to plastoquinone, a molecule nearly identical to ubiquinone. 7 However, when plants are exposed to excessive light, chlorophyll* reacts with triplet O 2 to form 1 O 2 and ground state chlorophyll. 8,9 Carotenoids within plants serve as reactive oxygen species (ROS) scavengers to protect chloroplasts from oxidative damage.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Photoreduction of ubiquinone to ubiquinol resembles the initial reactions of photosynthesis in which red light from the sun converts chlorophyll in chloroplasts to an excited triplet state, chlorophyll*. Under normal conditions, chlorophyll* transfers electrons to plastoquinone, a molecule nearly identical to ubiquinone . However, when plants are exposed to excessive light, chlorophyll* reacts with triplet O 2 to form 1 O 2 and ground state chlorophyll. , Carotenoids within plants serve as reactive oxygen species (ROS) scavengers to protect chloroplasts from oxidative damage.…”

Section: Introductionmentioning

confidence: 99%

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Photo-oxidation and Photoreduction of Catechols by Chlorophyll Metabolites and Methylene Blue

Landino

Shuckrow

Mooney

et al. 2022

Chem. Res. Toxicol.

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While plant-derived oxidants can protect cells from oxidative damage, limited research has examined the role of dietary chlorophyll. Photoreduction of ubiquinone by chlorophyll metabolites and red light has been reported in vitro and in animal models. Herein we examined photo-oxidation and photoreduction reactions of catechols, dopamine and hydrocaffeic acid. Photo-oxidation of dopamine by methylene blue and the chlorophyll metabolites pheophorbide A, chlorin e6 and sodium copper chlorophyllin was studied by monitoring aminochrome, the cyclized product of the dopamine o-quinone with its amine. Singlet oxygen scavengers including sodium azide, ascorbate and glutathione decreased aminochrome formation by methylene blue and pheophorbide A. Addition of EDTA, a tertiary amine electron donor, to the reaction of dopamine, photosensitizer and red light decreased aminochrome formation. Photoreduction of the dopamine o-quinone produced by mushroom tyrosinase was achieved by both methylene blue and pheophorbide A only when an electron donor was included. Due to limited solubility, photo-oxidation and photoreduction reactions by pheophorbide A required 5–7.5% dimethylformamide for optimal reactivity. Catalytic photoreduction of 2,3-dimethoxy-5-methyl-p-benzoquinone by methylene blue or pheophorbide A and tertiary amine electron donors was observed. Among the chlorophyll metabolites, pheophorbide A was more effective than chlorin e6 or sodium copper chlorophyllin in photo-oxidation of dopamine and photoreduction reactions. Singlet oxygen inhibited lactate dehydrogenase A activity, and higher molecular weight protein cross-links were observed on SDS-PAGE. Hydrocaffeic acid competed with lactate dehydrogenase A for reaction with singlet oxygen produced by methylene blue; however, no protection by hydrocaffeic acid (HCA) was observed when pheophorbide A was used. Cysteine modification of lactate dehydrogenase A by the o-quinone of hydrocaffeic acid was detected using a redox cycling stain. Inclusion of an electron donor decreased protein labeling.

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Section: ■ Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Photo-oxidation and Photoreduction of Catechols by Chlorophyll Metabolites and Methylene Blue

Landino

Shuckrow

Mooney

et al. 2022

Chem. Res. Toxicol.

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Interaction between Chlorophyll and Hydroquinone

Fujimori

Tavla

1965

Nature

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Reversible Light‐tnduced Single Electron Transfer Reactions Between Chlorophyll and Hydroquinone in Solution*

Banerjee

Tollin

1966

Photochem & Photobiology

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Abstract— EPR and optical studies demonstrate the occurrence of reversible temperature‐independent light‐induced single electron transfer reactions between chlorophyll (and pheophytin) and hydroquinone in degassed ethanol solutions. Oxygen is shown to quench this process, presumably by interacting with chlorophyll excited states. Pyridine and isoquino‐line increase the effectiveness of the hydroquinone as an electron donor to chlorophyll, probably by acting as bases to form hydroquinone anions (or perhaps ion‐pairs) which are more easily oxidized. Hydroquinone is found to be more effective in electron transfer than is benzoquinone, suggesting that the chlorophyll excited state is a better oxidizing agent than it is a reducing agent.

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Photochemical Oxidation and Reduction of Plastoquinone sensitized by Isolated Chlorophylls

Cited by 4 publications

References 11 publications

Photo-oxidation and Photoreduction of Catechols by Chlorophyll Metabolites and Methylene Blue

Photo-oxidation and Photoreduction of Catechols by Chlorophyll Metabolites and Methylene Blue

Interaction between Chlorophyll and Hydroquinone

Reversible Light‐tnduced Single Electron Transfer Reactions Between Chlorophyll and Hydroquinone in Solution*

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