Interactions of iodide ions with isolated photosystem 2 particles

Papageorgiou, George C.; Lagoyanni, T.

doi:10.1016/0003-9861(91)90369-t

Cited by 6 publications

(4 citation statements)

References 40 publications

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“…No kinetic constants were determined, although the authors estimated that V max and the quantum efficiency in I --reconstituted PSII were about two-thirds those in Cl -reconstituted PSII. Papageorgiou and Lagoyanni observed activation at low concentrations of Ifollowed by inhibition at higher concentrations in PSII lacking PsbP and PsbQ (23), similar to the data presented in Figure 1. Kinetic constants were again not reported, but the authors noted that the inhibition was reversible and occurred from a site preceding electron donation to Tyr Z, separate from the Clactivation site.…”

Section: Discussionsupporting

confidence: 85%

“…The activation by NaI was compared with the activation by NaCl, which at high concentrations produced a maximum activity that was about 5 times that produced by I -. This plot closely resembles data published previously by Papageorgiou and Lagoyanni (23), who used tetrabutylammonium as the counterion rather than sodium, and by Hasagawa and coworkers (30), who found a higher maximum rate of O 2 evolution relative to that for Clat low light intensities.…”

Section: Activation/inhibition By Iodide In the Absence Of Chloridesupporting

confidence: 89%

“…The D1 polypeptide is iodinated during turnover, but the D2 polypeptide is also labeled in the dark (20). When PsbP and PsbQ are removed, Ican activate O 2 evolution in the absence of Clbut is inhibitory at all concentrations in the presence of Cl - (23). Activating Ican also be reconstituted into the Clsite, with subsequent rebinding of the PsbP and PsbQ subunits (24).…”

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confidence: 99%

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Characteristics of Iodide Activation and Inhibition of Oxygen Evolution by Photosystem II

et al. 2005

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Oxygen evolution by photosystem II (PSII) is activated by chloride and other monovalent anions. In this study, the effects of iodide on oxygen evolution activity were investigated using PSII-enriched membrane fragments from spinach. In the absence of Cl(-), the dependence of oxygen evolution activity on I(-) concentration showed activation followed by inhibition in both intact PSII and NaCl-washed PSII, which lacked the PsbP and PsbQ subunits. Using a substrate inhibition model, the range of values of the Michaelis constant K(M) in intact PSII (0.5-1.5 mM) was smaller than that in NaCl-washed PSII (1.5-5 mM), whereas values of the inhibition constant K(I) in intact PSII (9-17 mM) were larger than those in NaCl-washed PSII (1-4 mM). Studies of I(-) inhibition of Cl(-)-activated oxygen evolution in intact PSII revealed that I(-) was primarily an uncompetitive inhibitor, with uncompetitive constant K(i)' = 37 mM and Cl(-)-competitive constant K(i) > 200 mM. This result indicated that the activating Cl(-) must be bound for inhibition to take place, which is consistent with the substrate inhibition model for I(-) activation. The S(2) state multiline and g = 4.1 EPR signals in NaCl-washed PSII were examined in the presence of 3 and 25 mM NaI, corresponding to I(-)-activated and I(-)-inhibited conditions, respectively. The two S(2) state signals were observed at both I(-) concentrations, indicating that I(-) substitutes for Cl(-) in formation of the signals and that advancement to the S(2) state was not prevented by high I(-) concentrations. A model is presented that incorporates the results of this study, including the action of both chloride and iodide.

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Section: Discussionsupporting

confidence: 85%

Section: Activation/inhibition By Iodide In the Absence Of Chloridesupporting

confidence: 89%

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confidence: 99%

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Characteristics of Iodide Activation and Inhibition of Oxygen Evolution by Photosystem II

et al. 2005

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“…Addition of Clto the iodination reaction mixture completely prevented iodination of the D 1 polypeptide, which suggests that the electron donor activity of Iis exerted from the site where cofactor anions activate the OEC. This conclusion was brought into question, however, by later results of Papagiorgiou and Lagoyanni (16), who reported that Iinterfered noncompetitively with the reactivation of salt-washed PS II by Cl -, and by results of Rashid and Homann (17), who concluded that Icould replace Cland support high rates of oxygen evolution, provided that the anion is bound only at the cofactor site in PS II and is not present in the bulk medium; i.e., Ibound at the Clsite appeared to be immune to oxidation.…”

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confidence: 97%

Activating Anions That Replace Cl^- in the O₂-Evolving Complex of Photosystem II Slow the Kinetics of the Terminal Step in Water Oxidation and Destabilize the S₂ and S₃ States

1999

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Photosystem II, the multisubunit protein complex that oxidizes water to O2, requires the inorganic cofactors Ca2+ and Cl- to exhibit optimal activity. Chloride can be replaced functionally by a small number of anionic cofactors (Br-, NO3-, NO2-, I-), but among these anions, only Br- is capable of restoring rates of oxygen evolution comparable to those observed with Cl-. UV absorption difference spectroscopy was utilized in the experiments described here as a probe to monitor donor side reactions in photosystem II in the presence of Cl- or surrogate anions. The rate of the final step of the water oxidation cycle was found to depend on the activating anion bound at the Cl- site, but the kinetics of this step did not limit the light-saturated rate of oxygen evolution. Instead, the lower oxygen evolution rates supported by surrogate anions appeared to be correlated with an instability of the higher oxidation states of the oxygen-evolving complex that was induced by addition of these anions. Reduction of these states takes place not only with I- but also with NO2- and to a lesser extent even with NO3- and Br- and is not related to the ability of these anions to bind at the Cl- binding site. Rather, it appears that these anions can attack higher oxidation states of the oxygen evolving complex from a second site that is not shielded by the extrinsic 17 and 23 kDa polypeptides and cause a one-electron reduction. The decrease of the oxygen evolution rate may result from accumulated damage to the reaction center protein by the one-electron oxidation product of the anion.

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The Cl− Requirement for Oxygen Evolution by Photosystem II Explored Using Enzyme Kinetics and EPR Spectroscopy

Haddy

Sheppard

Johnson

et al. 2017

Photosynthesis: Structures, Mechanisms, and Applications

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Interactions of iodide ions with isolated photosystem 2 particles

Cited by 6 publications

References 40 publications

Characteristics of Iodide Activation and Inhibition of Oxygen Evolution by Photosystem II

Characteristics of Iodide Activation and Inhibition of Oxygen Evolution by Photosystem II

Activating Anions That Replace Cl^- in the O₂-Evolving Complex of Photosystem II Slow the Kinetics of the Terminal Step in Water Oxidation and Destabilize the S₂ and S₃ States

The Cl− Requirement for Oxygen Evolution by Photosystem II Explored Using Enzyme Kinetics and EPR Spectroscopy

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Interactions of iodide ions with isolated photosystem 2 particles

Cited by 6 publications

References 40 publications

Characteristics of Iodide Activation and Inhibition of Oxygen Evolution by Photosystem II

Characteristics of Iodide Activation and Inhibition of Oxygen Evolution by Photosystem II

Activating Anions That Replace Cl- in the O2-Evolving Complex of Photosystem II Slow the Kinetics of the Terminal Step in Water Oxidation and Destabilize the S2 and S3 States

The Cl− Requirement for Oxygen Evolution by Photosystem II Explored Using Enzyme Kinetics and EPR Spectroscopy

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Activating Anions That Replace Cl^- in the O₂-Evolving Complex of Photosystem II Slow the Kinetics of the Terminal Step in Water Oxidation and Destabilize the S₂ and S₃ States