Anomalous Acceleration of the Photocycle in Photosynthetic Reaction Centers Inhibited on the Acceptor Side

L. Gerencsér, P. Maróti

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

The rate of the photocycle (quinone reduction cycle) was measured under continuous light excitation in an isolated reaction center protein of the photosynthetic bacterium Rhodobacter sphaeroides. The rate is determined by the slowest step of the photocycle, which could be the photochemistry (charge separation), the quinone/quinol and cytochrome c2+/c3+ exchanges, or proton delivery to the secondary quinone. The photocycle was driven by high light intensity of a laser diode (5 W/cm2 at 808 nm) to avoid light limitation of the observed rate. The fast turnover of the reaction center (up to 103 s-1) was slowed down by inhibition of the proton delivery to the secondary quinone by transition metal ions (Cd2+ and Ni2+), by mutation of a key protonatable group (L213Asp → Asn), or by use of low-affinity ubiquinone (UQ 0) to the secondary quinone binding site. Although in all of these cases the rate of turnover was 2-3 orders of magnitude less than that of the primary photochemistry marked light intensity dependence was observed. The rate of the photocycle increased from 7 s-1 (Ni2+, low light intensity) to 27 s-1 (high light intensity) at pH 8.4. The anomalous reacceleration is due to alternative events on the acceptor side induced by continuous excitation. We argue that the continuous excitation of the protein trapped in the reduced acceptor (QA -QB -) state produces short-lived reduced bacteriopheophytin (1 -) that delivers activation energy to anomalous changes on the acceptor side as second interquinone electron transfer before proton uptake or increase of the quinone dissociation constant.

Original languageEnglish
Pages (from-to)96-99
Number of pages4
JournalBiopolymers - Peptide Science Section
Volume74
Issue number1-2
DOIs
Publication statusPublished - May 2004

Fingerprint

Photosynthetic Reaction Center Complex Proteins
High intensity light
Light
Photochemical reactions
Proteins
Photochemistry
Protons
Proton transfer
Cytochromes c2
Binding sites
Hydroquinones
Transition metals
Metal ions
Semiconductor lasers
Rhodobacter sphaeroides
Ion exchange
Semiconductor Lasers
Bacteria
Ubiquinone
Activation energy

Keywords

  • Cytochrome photooxidation
  • Electron transfer
  • Proton uptake
  • Quinones
  • Transition metal ions

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)
  • Biochemistry
  • Biophysics

Cite this

Anomalous Acceleration of the Photocycle in Photosynthetic Reaction Centers Inhibited on the Acceptor Side. / Gerencsér, L.; Maróti, P.

In: Biopolymers - Peptide Science Section, Vol. 74, No. 1-2, 05.2004, p. 96-99.

Research output: Contribution to journalArticle

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