P680
 |
P680, or Photosystem II primary donor, (where P stands for pigment) is a group of pigments associated with photosystem II and consists of 4 chlorophyll a molecules[1]. These four molecules are excitonically coupled which means that they effectively act as a single entity, i.e. they are excited as if they were a single molecule. The 680 number is its absorption maximum in the red part of the visible spectrum (680 nm). The primary donor receives excitation energy either by absorbing a photon of suitable frequency (colour) or by excitation energy transfer from other chlorophylls within photosystem II. During excitation an electron is excited to a higher energy level. This electron is subsequently captured by the primary electron acceptor, a pheophytin molecule located within photosystem II near P680. The oxidized P680 (P680+) is subsequently reduced by an electron originating from water (via Oxygen evolving complex).
P680 is the strongest biological oxidizing agent known. It has an estimated redox potential of ~1.3 V[2]. This makes it possible to oxidize water during oxygenic photosynthesis.
See also
- P700.
.svg){kind=small} | This biochemistry article is a stub. You can help Wikipedia by expanding it. |
- ^ Raszewski G, Diner BA, Schlodder E and Renger T (2008) Spectroscopic properties of reaction center pigments in photosystem II core complexes: Revision of the multimer model. Biophys. J. 95:105-119
- ^ Rappaport F, Guergova-Kuras M, Nixon PJ, Diner BA and Lavergne J (2002): Kinetics and pathways of charge recombination in photosystem II. Biochemistry 41, 8518-8527.