Delayed fluorescence study on P*Q(A)→ P+Q(A)- charge separation energetics linked to protons and salt in reaction centers from Rhodobacter sphaeroides

Kinga Turzó, Gábor Laczkó, P. Maróti

Research output: Contribution to journalArticle

11 Citations (Scopus)

Abstract

The energetics of the first stable charge separated state, P Q(A)- relative to that of P*Q(A) was examined in isolated RC from Rhodobacter sphaeroides by delayed fluorescence. The temperature dependence of the delayed fluorescence indicates that the charge separation is a highly enthalpy-driven process (ΔH= - 818 ±20 meV at pH 8) and the free energy gap between P*Q(A) and P+Q(A)- drops with increasing pH (40 ± 4 meV between pH 6 and 10). The pH-dependence of the free energy change of the P+Q(A)- state runs parallel to the (integrated) net proton uptake due to the PQ(A)/P+Q(A)- redox change in a wide pH range and under different ionic conditions. Elevation of the ionic strength increases the delayed fluorescence intensity and decreases the (dark and light) pK(a) values as well as the light-induced ΔpK(a) changes of the protonatable groups of the protein. The observed dependence of the energetics of P+Q(A)- on the concentration and composition of mobile ions is discussed in terms of binding and screening of protonatable groups and surface charges as dominant modes of electrostatic interaction between RC and salt.

Original languageEnglish
Pages (from-to)235-240
Number of pages6
JournalPhotosynthesis Research
Volume55
Issue number2-3
Publication statusPublished - 1998

Fingerprint

Rhodobacter sphaeroides
protons
Protons
Salts
Fluorescence
fluorescence
salts
Free energy
Surface charge
Coulomb interactions
Ionic strength
Enthalpy
Screening
Energy gap
Light
electrostatic interactions
Ions
energy
ionic strength
enthalpy

Keywords

  • Bacterial photosynthesis
  • Delayed fluorescence
  • Ionic screening
  • Proton binding
  • Reaction center

ASJC Scopus subject areas

  • Plant Science

Cite this

Delayed fluorescence study on P*Q(A)→ P+Q(A)- charge separation energetics linked to protons and salt in reaction centers from Rhodobacter sphaeroides. / Turzó, Kinga; Laczkó, Gábor; Maróti, P.

In: Photosynthesis Research, Vol. 55, No. 2-3, 1998, p. 235-240.

Research output: Contribution to journalArticle

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AB - The energetics of the first stable charge separated state, P Q(A)- relative to that of P*Q(A) was examined in isolated RC from Rhodobacter sphaeroides by delayed fluorescence. The temperature dependence of the delayed fluorescence indicates that the charge separation is a highly enthalpy-driven process (ΔH= - 818 ±20 meV at pH 8) and the free energy gap between P*Q(A) and P+Q(A)- drops with increasing pH (40 ± 4 meV between pH 6 and 10). The pH-dependence of the free energy change of the P+Q(A)- state runs parallel to the (integrated) net proton uptake due to the PQ(A)/P+Q(A)- redox change in a wide pH range and under different ionic conditions. Elevation of the ionic strength increases the delayed fluorescence intensity and decreases the (dark and light) pK(a) values as well as the light-induced ΔpK(a) changes of the protonatable groups of the protein. The observed dependence of the energetics of P+Q(A)- on the concentration and composition of mobile ions is discussed in terms of binding and screening of protonatable groups and surface charges as dominant modes of electrostatic interaction between RC and salt.

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