Effects of azide on the S2 state EPR signals from Photosystem II

Alice Haddy, R. Allen Kimel, Rebecca Thomas

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

The anion azide, N3-, has been previously found to be an inhibitor of oxygen evolution by Photosystem II (PS II) of higher plants. With respect to chloride activation, azide acts primarily as a competitive inhibitor but uncompetitive inhibition also occurs [Haddy A, Hatchell JA, Kimel RA and Thomas R (1999) Biochemistry 38: 6104-6110]. In this study, the effects of azide on PS II-enriched thylakoid membranes were characterized by electron paramagnetic resonance (EPR) spectroscopy. Azide showed two distinguishable effects on the S2 state EPR signals. In the presence of chloride, which prevented competitive binding, azide suppressed the formation of the multiline and g = 4.1 signals concurrently, indicating that the normal S2 state was not reached. Signal suppression showed an azide concentration dependence that correlated with the fraction of PS II centers calculated to bind azide at the uncompetitive site, based on the previously determined inhibition constant. No evidence was found for an effect of azide on the Fe(II)Q(A)- signals at the concentrations used. This result is consistent with placement of the uncompetitive site on the donor side of PS II as suggested in the previous study. In chloride-depleted PS II-enriched membranes azide and fluoride showed similar effects on the S2 state EPR signals, including a notable increase and narrowing of the g = 4.1 signal. Comparable effects of other anions have been described previously and apparently take place through the chloride-competitive site. The two azide binding sites described here correlate with the results of other studies of Lewis base inhibitors.

Original languageEnglish (US)
Pages (from-to)35-45
Number of pages11
JournalPhotosynthesis research
Volume63
Issue number1
DOIs
StatePublished - Jan 1 2000

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azides
Photosystem II Protein Complex
Azides
electron paramagnetic resonance spectroscopy
Electron Spin Resonance Spectroscopy
photosystem II
Paramagnetic resonance
Chlorides
chlorides
anions
Anions
Lewis Bases
Membranes
Biochemistry
Thylakoids
Competitive Binding
fluorides
Fluorides
thylakoids
biochemistry

All Science Journal Classification (ASJC) codes

  • Biochemistry
  • Plant Science
  • Cell Biology

Cite this

Haddy, Alice ; Allen Kimel, R. ; Thomas, Rebecca. / Effects of azide on the S2 state EPR signals from Photosystem II. In: Photosynthesis research. 2000 ; Vol. 63, No. 1. pp. 35-45.
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Effects of azide on the S2 state EPR signals from Photosystem II. / Haddy, Alice; Allen Kimel, R.; Thomas, Rebecca.

In: Photosynthesis research, Vol. 63, No. 1, 01.01.2000, p. 35-45.

Research output: Contribution to journalArticle

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AB - The anion azide, N3-, has been previously found to be an inhibitor of oxygen evolution by Photosystem II (PS II) of higher plants. With respect to chloride activation, azide acts primarily as a competitive inhibitor but uncompetitive inhibition also occurs [Haddy A, Hatchell JA, Kimel RA and Thomas R (1999) Biochemistry 38: 6104-6110]. In this study, the effects of azide on PS II-enriched thylakoid membranes were characterized by electron paramagnetic resonance (EPR) spectroscopy. Azide showed two distinguishable effects on the S2 state EPR signals. In the presence of chloride, which prevented competitive binding, azide suppressed the formation of the multiline and g = 4.1 signals concurrently, indicating that the normal S2 state was not reached. Signal suppression showed an azide concentration dependence that correlated with the fraction of PS II centers calculated to bind azide at the uncompetitive site, based on the previously determined inhibition constant. No evidence was found for an effect of azide on the Fe(II)Q(A)- signals at the concentrations used. This result is consistent with placement of the uncompetitive site on the donor side of PS II as suggested in the previous study. In chloride-depleted PS II-enriched membranes azide and fluoride showed similar effects on the S2 state EPR signals, including a notable increase and narrowing of the g = 4.1 signal. Comparable effects of other anions have been described previously and apparently take place through the chloride-competitive site. The two azide binding sites described here correlate with the results of other studies of Lewis base inhibitors.

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