P680
{{refimprove|date=August 2021}}
P680, or photosystem II primary donor, is the reaction-center chlorophyll a molecular dimer associated with photosystem II in plants, algae, and cyanobacteria, and central to oxygenic photosynthesis.
Etymology
Its name is derived from the word “pigment” (P) and the presence of a major bleaching band centered around 680-685 nm in the flash-induced absorbance difference spectra of P680/ P680+•.Shigeru Itoh, S; Iwaki, M; Tomo, T; Satoh, K (1996). Dibromothymoquinone (DBMIB) replaces the function of QA at 77 K in the isolated photosystem II reaction center (Dl-D2-cytochrome 6559) complex: Difference spectrum of the P680+ (DBMIB") state. Plant Cell Physiol. 37(6): 833-839.
Components
The structure of P680 consists of a heterodimer of two distinct chlorophyll molecules,
referred to as P{{sub|D1}} and P{{sub|D2}}. This “special pair” forms an excitonic dimer that functions as a single unit, excited by light energy as if they were a single molecule.{{sfnp|Raszewski|Diner|Schlodder|Renger|2008|pp=105-119}}
Action and function
= Excitation =
P680 receives excitation energy either by directly absorbing a photon of suitable frequency or indirectly from other chlorophylls within photosystem II, thereby exciting an electron to a higher energy level. The resulting P680 with a loosened electron is designated as P680*, which is a strong reducing agent.
= Charge separation =
Following excitation, the loosened electron of P680* is taken up by the primary electron acceptor, a pheophytin molecule located within photosystem II near P680. During this transfer, P680* is ionized and oxidized, producing cationic P680{{sup|+}}.
= Recovery of P680 =
P680+ is the strongest biological oxidizing agent known, with an estimated redox potential of ~1.3 V.{{sfnp|Rappaport|Guergova-Kuras|Nixon|Diner|2002|pp=8518–8527}} This makes it possible to oxidize water during oxygenic photosynthesis. P680+ recovers its lost electron by oxidizing water via the oxygen-evolving complex, which regenerates P680.
See also
References
{{reflist|}}
Bibliography
{{refbegin|2}}
- {{cite journal |last1=Raszewski |first1=Grzegorz |last2=Diner |first2=Bruce A. |last3=Schlodder |first3=Eberhard |last4=Renger |first4=Thomas | title = Spectroscopic properties of reaction center pigments in photosystem II core complexes: Revision of the multimer model | name-list-style = amp | journal = Biophys. J. | year = 2008 | volume = 95 |issue=1 | pages = 105–119 | doi = 10.1529/biophysj.107.123935| pmid = 18339736 | pmc = 2426664 |bibcode=2008BpJ....95..105R }}
- {{cite journal |last1=Rappaport |first1=F |last2=Guergova-Kuras |first2=M |last3=Nixon |first3=PJ |last4=Diner |first4=BA |last5=Lavergne |first5=J|year=2002|title=Kinetics and pathways of charge recombination in photosystem II|journal=Biochemistry|volume=41|issue=26 |doi=10.1021/bi025725p |pages=8518–8527|url=http://www.ibpc.fr/UMR7141/web_lab/2002/Rappaport02.pdf|pmid=12081503}}
{{refend}}
{{photosynthesis-stub}}