Mechanism of photoinhibition of photosynthetic water oxidation by Cl- depletion and F- substitution

Oxidation of a protein residue

M. Baumgarten, G Charles Dismukes, G. C. Dismukes

Research output: Contribution to journalArticle

93 Citations (Scopus)

Abstract

New evidence on the chloride requirement for photosynthetic O2 evolution has indicated that Cl- facilitates oxidation of the manganese cluster by the photosystem II (PSII) Tyr-Z+ radical. Illumination above 250 K of spinach PSII centers which are inhibited in O2 evolution by either Cl- depletion or F- substitution produces a new EPR signal which has magnetic characteristics similar to one recently discovered in samples inhibited by depletion of Ca2+ only [Boussac et al. (1989) Biochemistry 28, 8984; Sivaraja et al. (1989) Biochemistry 28, 9459]. The physiological roles of Cl- and Ca2+ in water oxidation are thus linked. The characteristics include a nearly isotropic g = 2.00 ± 0.005, a symmetric line shape with line width = 16 ± 2 mT, almost stoichiometric spin concentration relative to Try-D+ = 0.6 ± 0.3 spin/PSII, very rapid spin relaxation at all temperatures measured down to 6 K, and an undetectable change in magnetic susceptibility upon formation (B 2). The signal appears to originate from a spin doublet (radical) in magnetic dipolar contact with a transition-metal ion, most probably a photooxidized protein residue within 10 Å of the Mn cluster (Mn-proximal radical). It is distinct from the three other protein-bound radical-type electron donors found in the PSII reaction center: Tyr-D+, Tyr-Z+, and C+. This signal photoaccumulates to a stable level under continuous illumination at 270 K and decays only after illumination stops. Illumination below 250 K suppresses both photooxidation of the Mn cluster and formation of the Mn-proximal radical, with parallel formation of the C+ radical (0.9-mT line width) in place of the usual Tyr-Z+ signal. Either Tyr-Z+ or the Mn cluster are candidates for oxidation of the Mn-proximal protein residue above 250 K. Single-turnover laser-flash EPR studies above 250 K show that the new signal appears after two flashes, photoaccumulates in the S3′ state, and is blocked from further turnover. Nearly fully recovery of water oxidation, low-temperature electron transfer (Mn → Tyr-Z+), and loss of the Mn-proximal EPR signal occur upon Cl- reconstitution. These observations support earlier studies suggesting that photooxidation of a species other than Mn may occur during normal photochemistry in the native enzyme. F--substituted PSII centers exhibit a large increase in magnetic susceptibility for the S1′ → S2′ state transition that is indistinguishable from Cl--reconstituted samples, indicative of an equivalent decrease in magnetic coupling between the Mn ions of the cluster for both halides. Therefore, the S1 → S2 oxidation step in F--substituted centers cannot occur at a magnetically isolated Mn(III) monomer site remote from the Mn cluster, as had been suggested earlier by others on the basis of formation of an EPR signal at g = 4.1. The large increase in magnetic susceptibility is consistent with simultaneous Mn oxidation and magnetic uncoupling of a tri- or tetranuclear Mn cluster on the S1 → S2 transition [Sivaraja et al. (1989) J. Am. Chem. Soc. 111, 3221].

Original languageEnglish
Pages (from-to)10814-10822
Number of pages9
JournalBiochemistry
Volume29
Issue number48
Publication statusPublished - 1990

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Photosystem II Protein Complex
Lighting
Substitution reactions
Oxidation
Paramagnetic resonance
Water
Magnetic susceptibility
Biochemistry
Proteins
Photooxidation
Linewidth
Electrons
Ions
Photochemistry
Temperature
Spinacia oleracea
Magnetic couplings
Manganese
Photochemical reactions
Electron temperature

ASJC Scopus subject areas

  • Biochemistry

Cite this

Mechanism of photoinhibition of photosynthetic water oxidation by Cl- depletion and F- substitution : Oxidation of a protein residue. / Baumgarten, M.; Dismukes, G Charles; Dismukes, G. C.

In: Biochemistry, Vol. 29, No. 48, 1990, p. 10814-10822.

Research output: Contribution to journalArticle

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title = "Mechanism of photoinhibition of photosynthetic water oxidation by Cl- depletion and F- substitution: Oxidation of a protein residue",
abstract = "New evidence on the chloride requirement for photosynthetic O2 evolution has indicated that Cl- facilitates oxidation of the manganese cluster by the photosystem II (PSII) Tyr-Z+ radical. Illumination above 250 K of spinach PSII centers which are inhibited in O2 evolution by either Cl- depletion or F- substitution produces a new EPR signal which has magnetic characteristics similar to one recently discovered in samples inhibited by depletion of Ca2+ only [Boussac et al. (1989) Biochemistry 28, 8984; Sivaraja et al. (1989) Biochemistry 28, 9459]. The physiological roles of Cl- and Ca2+ in water oxidation are thus linked. The characteristics include a nearly isotropic g = 2.00 ± 0.005, a symmetric line shape with line width = 16 ± 2 mT, almost stoichiometric spin concentration relative to Try-D+ = 0.6 ± 0.3 spin/PSII, very rapid spin relaxation at all temperatures measured down to 6 K, and an undetectable change in magnetic susceptibility upon formation (B 2). The signal appears to originate from a spin doublet (radical) in magnetic dipolar contact with a transition-metal ion, most probably a photooxidized protein residue within 10 {\AA} of the Mn cluster (Mn-proximal radical). It is distinct from the three other protein-bound radical-type electron donors found in the PSII reaction center: Tyr-D+, Tyr-Z+, and C+. This signal photoaccumulates to a stable level under continuous illumination at 270 K and decays only after illumination stops. Illumination below 250 K suppresses both photooxidation of the Mn cluster and formation of the Mn-proximal radical, with parallel formation of the C+ radical (0.9-mT line width) in place of the usual Tyr-Z+ signal. Either Tyr-Z+ or the Mn cluster are candidates for oxidation of the Mn-proximal protein residue above 250 K. Single-turnover laser-flash EPR studies above 250 K show that the new signal appears after two flashes, photoaccumulates in the S3′ state, and is blocked from further turnover. Nearly fully recovery of water oxidation, low-temperature electron transfer (Mn → Tyr-Z+), and loss of the Mn-proximal EPR signal occur upon Cl- reconstitution. These observations support earlier studies suggesting that photooxidation of a species other than Mn may occur during normal photochemistry in the native enzyme. F--substituted PSII centers exhibit a large increase in magnetic susceptibility for the S1′ → S2′ state transition that is indistinguishable from Cl--reconstituted samples, indicative of an equivalent decrease in magnetic coupling between the Mn ions of the cluster for both halides. Therefore, the S1 → S2 oxidation step in F--substituted centers cannot occur at a magnetically isolated Mn(III) monomer site remote from the Mn cluster, as had been suggested earlier by others on the basis of formation of an EPR signal at g = 4.1. The large increase in magnetic susceptibility is consistent with simultaneous Mn oxidation and magnetic uncoupling of a tri- or tetranuclear Mn cluster on the S1 → S2 transition [Sivaraja et al. (1989) J. Am. Chem. Soc. 111, 3221].",
author = "M. Baumgarten and Dismukes, {G Charles} and Dismukes, {G. C.}",
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TY - JOUR

T1 - Mechanism of photoinhibition of photosynthetic water oxidation by Cl- depletion and F- substitution

T2 - Oxidation of a protein residue

AU - Baumgarten, M.

AU - Dismukes, G Charles

AU - Dismukes, G. C.

PY - 1990

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N2 - New evidence on the chloride requirement for photosynthetic O2 evolution has indicated that Cl- facilitates oxidation of the manganese cluster by the photosystem II (PSII) Tyr-Z+ radical. Illumination above 250 K of spinach PSII centers which are inhibited in O2 evolution by either Cl- depletion or F- substitution produces a new EPR signal which has magnetic characteristics similar to one recently discovered in samples inhibited by depletion of Ca2+ only [Boussac et al. (1989) Biochemistry 28, 8984; Sivaraja et al. (1989) Biochemistry 28, 9459]. The physiological roles of Cl- and Ca2+ in water oxidation are thus linked. The characteristics include a nearly isotropic g = 2.00 ± 0.005, a symmetric line shape with line width = 16 ± 2 mT, almost stoichiometric spin concentration relative to Try-D+ = 0.6 ± 0.3 spin/PSII, very rapid spin relaxation at all temperatures measured down to 6 K, and an undetectable change in magnetic susceptibility upon formation (B 2). The signal appears to originate from a spin doublet (radical) in magnetic dipolar contact with a transition-metal ion, most probably a photooxidized protein residue within 10 Å of the Mn cluster (Mn-proximal radical). It is distinct from the three other protein-bound radical-type electron donors found in the PSII reaction center: Tyr-D+, Tyr-Z+, and C+. This signal photoaccumulates to a stable level under continuous illumination at 270 K and decays only after illumination stops. Illumination below 250 K suppresses both photooxidation of the Mn cluster and formation of the Mn-proximal radical, with parallel formation of the C+ radical (0.9-mT line width) in place of the usual Tyr-Z+ signal. Either Tyr-Z+ or the Mn cluster are candidates for oxidation of the Mn-proximal protein residue above 250 K. Single-turnover laser-flash EPR studies above 250 K show that the new signal appears after two flashes, photoaccumulates in the S3′ state, and is blocked from further turnover. Nearly fully recovery of water oxidation, low-temperature electron transfer (Mn → Tyr-Z+), and loss of the Mn-proximal EPR signal occur upon Cl- reconstitution. These observations support earlier studies suggesting that photooxidation of a species other than Mn may occur during normal photochemistry in the native enzyme. F--substituted PSII centers exhibit a large increase in magnetic susceptibility for the S1′ → S2′ state transition that is indistinguishable from Cl--reconstituted samples, indicative of an equivalent decrease in magnetic coupling between the Mn ions of the cluster for both halides. Therefore, the S1 → S2 oxidation step in F--substituted centers cannot occur at a magnetically isolated Mn(III) monomer site remote from the Mn cluster, as had been suggested earlier by others on the basis of formation of an EPR signal at g = 4.1. The large increase in magnetic susceptibility is consistent with simultaneous Mn oxidation and magnetic uncoupling of a tri- or tetranuclear Mn cluster on the S1 → S2 transition [Sivaraja et al. (1989) J. Am. Chem. Soc. 111, 3221].

AB - New evidence on the chloride requirement for photosynthetic O2 evolution has indicated that Cl- facilitates oxidation of the manganese cluster by the photosystem II (PSII) Tyr-Z+ radical. Illumination above 250 K of spinach PSII centers which are inhibited in O2 evolution by either Cl- depletion or F- substitution produces a new EPR signal which has magnetic characteristics similar to one recently discovered in samples inhibited by depletion of Ca2+ only [Boussac et al. (1989) Biochemistry 28, 8984; Sivaraja et al. (1989) Biochemistry 28, 9459]. The physiological roles of Cl- and Ca2+ in water oxidation are thus linked. The characteristics include a nearly isotropic g = 2.00 ± 0.005, a symmetric line shape with line width = 16 ± 2 mT, almost stoichiometric spin concentration relative to Try-D+ = 0.6 ± 0.3 spin/PSII, very rapid spin relaxation at all temperatures measured down to 6 K, and an undetectable change in magnetic susceptibility upon formation (B 2). The signal appears to originate from a spin doublet (radical) in magnetic dipolar contact with a transition-metal ion, most probably a photooxidized protein residue within 10 Å of the Mn cluster (Mn-proximal radical). It is distinct from the three other protein-bound radical-type electron donors found in the PSII reaction center: Tyr-D+, Tyr-Z+, and C+. This signal photoaccumulates to a stable level under continuous illumination at 270 K and decays only after illumination stops. Illumination below 250 K suppresses both photooxidation of the Mn cluster and formation of the Mn-proximal radical, with parallel formation of the C+ radical (0.9-mT line width) in place of the usual Tyr-Z+ signal. Either Tyr-Z+ or the Mn cluster are candidates for oxidation of the Mn-proximal protein residue above 250 K. Single-turnover laser-flash EPR studies above 250 K show that the new signal appears after two flashes, photoaccumulates in the S3′ state, and is blocked from further turnover. Nearly fully recovery of water oxidation, low-temperature electron transfer (Mn → Tyr-Z+), and loss of the Mn-proximal EPR signal occur upon Cl- reconstitution. These observations support earlier studies suggesting that photooxidation of a species other than Mn may occur during normal photochemistry in the native enzyme. F--substituted PSII centers exhibit a large increase in magnetic susceptibility for the S1′ → S2′ state transition that is indistinguishable from Cl--reconstituted samples, indicative of an equivalent decrease in magnetic coupling between the Mn ions of the cluster for both halides. Therefore, the S1 → S2 oxidation step in F--substituted centers cannot occur at a magnetically isolated Mn(III) monomer site remote from the Mn cluster, as had been suggested earlier by others on the basis of formation of an EPR signal at g = 4.1. The large increase in magnetic susceptibility is consistent with simultaneous Mn oxidation and magnetic uncoupling of a tri- or tetranuclear Mn cluster on the S1 → S2 transition [Sivaraja et al. (1989) J. Am. Chem. Soc. 111, 3221].

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