Abstract
The role of chloride in photosystem II (PSII) is unclear. Several monovalent anions compete for the Cl- site(s) in PSII, and some even support activity. NO2 - has been reported to be an activator in Cl--depleted PSII membranes. In this paper, we report a detailed investigation of the chemistry of NO2 - with PSII. NO2 - is shown to inhibit PSII activity, and the effects on the donor side as well as the acceptor side are characterized using steady-state O2-evolution assays, electron paramagnetic resonance (EPR) spectroscopy, electron-transfer assays, and flash-induced polarographic O2 yield measurements. Enzyme kinetics analysis shows multiple sites of NO2 - inhibition in PSII with significant inhibition of oxygen evolution at 2 -. By EPR spectroscopy, the yield of the S2 state remains unchanged up to 15 mM NO 2 -. However, the S2-state g = 4.1 signal is favored over the g = 2 multiline signal with increasing NO2 - concentrations. This could indicate competition of NO 2 - for the Cl- site at higher NO 2 - concentrations. In addition to the donor-side chemistry, there is clear evidence of an acceptor-side effect of NO 2 -. The g = 1.9 Fe(II)-QA -• signal is replaced by a broad g = 1.6 signal in the presence of NO 2 -. Additionally, a g = 1.8 Fe(II)-Q-• signal is present in the dark, indicating the formation of a NO2 --bound Fe(II)-QB -• species in the dark. Electron-transfer assays suggest that the inhibitory effect of NO 2 - on the activity of PSII is largely due to the donor-side chemistry of NO2 -. UV-visible spectroscopy and flash-induced polarographic O2 yield measurements indicate that NO2 - is oxidized by the oxygen-evolving complex in the higher S states, contributing to the donor-side inhibition by NO 2 -.
| Original language | English |
|---|---|
| Pages (from-to) | 3781-3789 |
| Number of pages | 9 |
| Journal | Biochemistry |
| Volume | 52 |
| Issue number | 21 |
| DOIs | |
| Publication status | Published - May 28 2013 |
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- Biochemistry
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Investigation of the inhibitory effect of nitrite on photosystem II. / Pokhrel, Ravi; Brudvig, Gary W.
In: Biochemistry, Vol. 52, No. 21, 28.05.2013, p. 3781-3789.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Investigation of the inhibitory effect of nitrite on photosystem II
AU - Pokhrel, Ravi
AU - Brudvig, Gary W
PY - 2013/5/28
Y1 - 2013/5/28
N2 - The role of chloride in photosystem II (PSII) is unclear. Several monovalent anions compete for the Cl- site(s) in PSII, and some even support activity. NO2 - has been reported to be an activator in Cl--depleted PSII membranes. In this paper, we report a detailed investigation of the chemistry of NO2 - with PSII. NO2 - is shown to inhibit PSII activity, and the effects on the donor side as well as the acceptor side are characterized using steady-state O2-evolution assays, electron paramagnetic resonance (EPR) spectroscopy, electron-transfer assays, and flash-induced polarographic O2 yield measurements. Enzyme kinetics analysis shows multiple sites of NO2 - inhibition in PSII with significant inhibition of oxygen evolution at 2 -. By EPR spectroscopy, the yield of the S2 state remains unchanged up to 15 mM NO 2 -. However, the S2-state g = 4.1 signal is favored over the g = 2 multiline signal with increasing NO2 - concentrations. This could indicate competition of NO 2 - for the Cl- site at higher NO 2 - concentrations. In addition to the donor-side chemistry, there is clear evidence of an acceptor-side effect of NO 2 -. The g = 1.9 Fe(II)-QA -• signal is replaced by a broad g = 1.6 signal in the presence of NO 2 -. Additionally, a g = 1.8 Fe(II)-Q-• signal is present in the dark, indicating the formation of a NO2 --bound Fe(II)-QB -• species in the dark. Electron-transfer assays suggest that the inhibitory effect of NO 2 - on the activity of PSII is largely due to the donor-side chemistry of NO2 -. UV-visible spectroscopy and flash-induced polarographic O2 yield measurements indicate that NO2 - is oxidized by the oxygen-evolving complex in the higher S states, contributing to the donor-side inhibition by NO 2 -.
AB - The role of chloride in photosystem II (PSII) is unclear. Several monovalent anions compete for the Cl- site(s) in PSII, and some even support activity. NO2 - has been reported to be an activator in Cl--depleted PSII membranes. In this paper, we report a detailed investigation of the chemistry of NO2 - with PSII. NO2 - is shown to inhibit PSII activity, and the effects on the donor side as well as the acceptor side are characterized using steady-state O2-evolution assays, electron paramagnetic resonance (EPR) spectroscopy, electron-transfer assays, and flash-induced polarographic O2 yield measurements. Enzyme kinetics analysis shows multiple sites of NO2 - inhibition in PSII with significant inhibition of oxygen evolution at 2 -. By EPR spectroscopy, the yield of the S2 state remains unchanged up to 15 mM NO 2 -. However, the S2-state g = 4.1 signal is favored over the g = 2 multiline signal with increasing NO2 - concentrations. This could indicate competition of NO 2 - for the Cl- site at higher NO 2 - concentrations. In addition to the donor-side chemistry, there is clear evidence of an acceptor-side effect of NO 2 -. The g = 1.9 Fe(II)-QA -• signal is replaced by a broad g = 1.6 signal in the presence of NO 2 -. Additionally, a g = 1.8 Fe(II)-Q-• signal is present in the dark, indicating the formation of a NO2 --bound Fe(II)-QB -• species in the dark. Electron-transfer assays suggest that the inhibitory effect of NO 2 - on the activity of PSII is largely due to the donor-side chemistry of NO2 -. UV-visible spectroscopy and flash-induced polarographic O2 yield measurements indicate that NO2 - is oxidized by the oxygen-evolving complex in the higher S states, contributing to the donor-side inhibition by NO 2 -.
UR - http://www.scopus.com/inward/record.url?scp=84878320480&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84878320480&partnerID=8YFLogxK
U2 - 10.1021/bi400206q
DO - 10.1021/bi400206q
M3 - Article
C2 - 23631466
AN - SCOPUS:84878320480
VL - 52
SP - 3781
EP - 3789
JO - Biochemistry
JF - Biochemistry
SN - 0006-2960
IS - 21
ER -