Water, water everywhere, and its remarkable chemistry

Biochim Biophys Acta. 2004 Apr 12;1655(1-3):123-32. doi: 10.1016/j.bbabio.2003.10.011.


Photosystem II (PSII), the multisubunit pigment-protein complex localised in the thylakoid membranes of oxygenic photosynthetic organisms, uses light energy to drive a series of remarkable reactions leading to the oxidation of water. The products of this oxidation are dioxygen, which is released to the atmosphere, and reducing equivalents destined to reduce carbon dioxide to organic molecules. The water oxidation occurs at catalytic sites composed of four manganese atoms (Mn(4)-cluster) and powered by the redox potential of an oxidised chlorophyll a molecule (P680(*+)). Gerald T (Jerry) Babcock and colleagues showed that electron/proton transfer processes from substrate water to P680(*+) involved a tyrosine residue (Y(Z)) and proposed an attractive reaction mechanism for the direct involvement of Y(Z) in the chemistry of water oxidation. The 'hydrogen-atom abstract/metalloradical' mechanism he formulated is an expression of his genius and a highlight of his many other outstanding contributions to photosynthesis research. A structural basis for Jerry's model is now being revealed by X-ray crystallography.

Publication types

  • Historical Article
  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Electron Spin Resonance Spectroscopy
  • History, 18th Century
  • History, 19th Century
  • History, 20th Century
  • Manganese / chemistry
  • Models, Molecular
  • Oxidation-Reduction
  • Photosystem II Protein Complex / chemistry
  • Photosystem II Protein Complex / history
  • Photosystem II Protein Complex / metabolism
  • Tyrosine / analogs & derivatives*
  • Tyrosine / chemistry
  • Water / chemistry*
  • Water / metabolism*


  • Photosystem II Protein Complex
  • tyrosyl radical Y(D)
  • tyrosyl radical YZ
  • Water
  • Tyrosine
  • Manganese