Electron, proton and hydrogen-atom transfers in photosynthetic water oxidation

Cecilia Tommos, L. Sun, P. Fromme, L. Hammarström, C. Zhang, S. Styring, A. W. Rutherford

Research output: Contribution to journalArticlepeer-review

37 Scopus citations


When photosynthetic organisms developed so that they could use water as an electron source to reduce carbon dioxide, the stage was set for efficient proliferation. Algae and plants spread globally and provided the foundation for our atmosphere and for O2-based chemistry in biological systems. Light-driven water oxidation is catalysed by photosystem II, the active site of which contains a redox-active tyrosine denoted YZ, a tetramanganese cluster, calcium and chloride. In 1995, Gerald Babcock and co-workers presented the hypothesis that photosynthetic water oxidation occurs as a metallo-radical catalysed process. In this model, the oxidized tyrosine radical is generated by coupled proton/electron transfer and re-reduced by abstracting hydrogen atoms from substrate water or hydroxide-ligated to the manganese cluster. The proposed function of YZ requires proton transfer from the tyrosine site upon oxidation. The oxidation mechanism of YZ in an inhibited and O2-evolving photosystem II is discussed. Domino-deprotonation from YZ to the bulk solution is shown to be consistent with a variety of data obtained on metal-depleted samples. Experimental data that suggest that the oxidation of YZ in O2-evolving samples is coupled to proton transfer in a hydrogen-bonding network are described. Finally, a dielectric-dependent model for the proton release that is associated with the catalytic cycle of photosystem II is discussed.

Original languageEnglish (US)
Pages (from-to)1383-1394
Number of pages12
JournalPhilosophical Transactions of the Royal Society B: Biological Sciences
Issue number1426
StatePublished - Oct 29 2002
Externally publishedYes


  • Oxygen-evolving complex
  • Photosynthetic water oxidation
  • Photosystem II
  • Redox-active tyrosine
  • Tyrosine radical

ASJC Scopus subject areas

  • General Biochemistry, Genetics and Molecular Biology
  • General Agricultural and Biological Sciences


Dive into the research topics of 'Electron, proton and hydrogen-atom transfers in photosynthetic water oxidation'. Together they form a unique fingerprint.

Cite this