The oxygen-evolving complex

The multiline spectrum shows some resemblance to that of a mixed valence cluster Mn - Mn or Mn - Mn [88,89,97] and with a computer simulation of a tetramer spectrum such as 3Mn - Mn [90]. Precise agreement, however, is lacking so far. The form and number of the lines depend on the period of dark adaptation and the illumination temperature and are sensitive to the presence of inhibitors of O2 evolution [91,92]. The signal is orientation-dependent, i.e. it has a fixed geometry with respect to the membrane [93]. 

Several interpretations of the two (perhaps even more) forms of the multiline signal have been advanced, making use of the temperature dependence of its intensity [91,94-98]. Further work may well resolve the still existing ambiguities and unexplained spectral forms, and allow a much deeper insight into the mechanism of oxygen evolution. 

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The oxygen-evolving complex of the thylakoid membrane of plant cells and of photosynthetic bacteria catalyzes the reaction shown in Equation (10) ... 

Fig. 19. One of the structures included in an extensive evaluation study of magnetic and spectroscopic properties for models of the S2 state of the oxygen evolving complex.

The four electrons abstracted from water do not pass directly to P680+, which can accept only one electron at a time. Instead, a remarkable molecular device, the oxygen-evolving complex (also called the watersplitting complex), passes four electrons one at a... 

Because the four protons produced in this reaction are released into the thylakoid lumen, the oxygen-evolving complex acts as a proton pump, driven by electron transfer. The sum of Equations 19-12 through 19-15 is... 

A well-illustrated introduction to the oxygen-evolving complex of plants. 

Rutherford, A. W., Photosystem II, the water-splitting enzyme. Trends Biochem. Sci. 14 227, 1989. A readable account of current results and speculations on the oxygen-evolving complex. 

The invention of aerobic photosynthesis, the light-driven oxidation of water to oxygen, stands as one of the pivotal evolutionary innovations in the history of life on Earth. The process is carried out only at the oxygen-evolving complex (OEC) of PSII in plants and algae, as well as in cyanobacteria. Despite the biological uniqueness of water oxidation to 02, several of the core proteins of PSII have homologues in the so-called type I and type II anaerobic photosynthetic reaction... 

Raymond J, Blankenship RE. The origin of the oxygen-evolving complex. Coord Chem Rev 2008 252 377-83. 

Kulik LV, Epel B, Lubitz W, Messinger J. Electronic structure of the MnRJxCa cluster in the So and S2 states of the oxygen-evolving complex of photosystem II based on pulse 55Mn ENDOR and EPR spectroscopy. J Am Chem Soc. 2007 129(44) 13421-35. 

Styring S, Rutherford AW. In the oxygen-evolving complex of photosystem II the So state is oxidized to the Si state by D+ (signal IIsiow). Biochemistry. 1987 26(9) 2401-5. 

Ames W, Pantazis DA, Krewald V, et al. Theoretical evaluation of structural models of the S2 state in the oxygen evolving complex of photosystem II protonation states and magnetic interactions. J Am Chem Soc. 2011 133(49) 19743-57. 

Robblee, JH, Messinger, J, Cinco, RM, et al. The Mn cluster in the So state of the oxygen-evolving complex of photosystem II studied by EXAFS spectroscopy are there three Di-p-oxo-bridged Mn2 moieties in the tetranuclear Mn complex J Am Chem Soc. 2002 124(25) 7459-71. 

Liang WC, Roelofs TA, Cinco RM, et al. Structural change of the Mn cluster during the S2 —> S3 state transition of the oxygen-evolving complex of photosystem II. Does it reflect the onset of water/substrate oxidation Determination by Mn X-ray absorption spectroscopy. J Am Chem Soc. 2000 122(14) 3 399 412. 

Pantazis DA, Ames W, Cox N, Lubitz W, Neese F. Two interconvertible structures that explain the spectroscopic properties of the oxygen evolving complex of photosystem II in the S2 state. Angew Chem Int Ed 2012 51(39) 9935-40. 

Kanady JS, Tsui EY, Day MW, Agapie T. A synthetic model of the MnK a subsite of the oxygen-evolving complex in photosystem II. Science. 2011 333 733-6. 

Chu, H.A., Sackett, H., and Babcock, G.T. (2000) Identification of a Mn-O-Mn cluster vibrational mode of the oxygen-evolving complex in photosystem II by low-frequency FTIR spectroscopy, Biochemistry 39, 14371-14376. 

Hanley, J., Sarrou, J., and Petrouleas, V. (2000) Orientation of the Mn(II)-Mn(II) dimere wwhich result from the reduction of the oxygen-evolving complex of Photosysem II by NO an electron paramagnetic resonance study, Biochemistry 39, 15441-15445. 

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