Thermodynamically accurate modeling of the catalytic cycle of photosynthetic oxygen evolution

A mathematical solution to asymmetric Markov chains

David J. Vinyard, Chase E. Zachary, Gennady Ananyev, G Charles Dismukes

Research output: Contribution to journalArticle

17 Citations (Scopus)

Abstract

Forty-three years ago, Kok and coworkers introduced a phenomenological model describing period-four oscillations in O2 flash yields during photosynthetic water oxidation (WOC), which had been first reported by Joliot and coworkers. The original two-parameter Kok model was subsequently extended in its level of complexity to better simulate diverse data sets, including intact cells and isolated PSII-WOCs, but at the expense of introducing physically unrealistic assumptions necessary to enable numerical solutions. To date, analytical solutions have been found only for symmetric Kok models (inefficiencies are equally probable for all intermediates, called "S-states"). However, it is widely accepted that S-state reaction steps are not identical and some are not reversible (by thermodynamic restraints) thereby causing asymmetric cycles. We have developed a mathematically more rigorous foundation that eliminates unphysical assumptions known to be in conflict with experiments and adopts a new experimental constraint on solutions. This new algorithm termed STEAMM for S-state Transition Eigenvalues of Asymmetric Markov Models enables solutions to models having fewer adjustable parameters and uses automated fitting to experimental data sets, yielding higher accuracy and precision than the classic Kok or extended Kok models. This new tool provides a general mathematical framework for analyzing damped oscillations arising from any cycle period using any appropriate Markov model, regardless of symmetry. We illustrate applications of STEAMM that better describe the intrinsic inefficiencies for photon-to-charge conversion within PSII-WOCs that are responsible for damped period-four and period-two oscillations of flash O2 yields across diverse species, while using simpler Markov models free from unrealistic assumptions.

Original languageEnglish
Pages (from-to)861-868
Number of pages8
JournalBiochimica et Biophysica Acta - Bioenergetics
Volume1827
Issue number7
DOIs
Publication statusPublished - Jul 2013

Fingerprint

Markov Chains
Markov processes
Oxygen
Statistical Models
Photons
Thermodynamics
Water
Datasets
Oxidation

Keywords

  • Kok model
  • Markov chain
  • Oxygen evolution
  • Photosynthetic efficiency
  • Photosystem II

ASJC Scopus subject areas

  • Biochemistry
  • Biophysics
  • Cell Biology

Cite this

Thermodynamically accurate modeling of the catalytic cycle of photosynthetic oxygen evolution : A mathematical solution to asymmetric Markov chains. / Vinyard, David J.; Zachary, Chase E.; Ananyev, Gennady; Dismukes, G Charles.

In: Biochimica et Biophysica Acta - Bioenergetics, Vol. 1827, No. 7, 07.2013, p. 861-868.

Research output: Contribution to journalArticle

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