- Source: P680
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+•.
Components
The structure of P680 consists of a heterodimer of two distinct chlorophyll molecules,
referred to as PD1 and PD2. This “special pair” forms an excitonic dimer that functions as a single unit, excited by light energy as if they were a single molecule.
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+.
= Recovery of P680
=P680+ is the strongest biological oxidizing agent known, with an estimated redox potential of ~1.3 V. 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
P700
Photosystem I
Photosystem II
References
Bibliography
Kata Kunci Pencarian:
- Klorofil
- Fotosintesis
- P680
- Light-dependent reactions
- Chlorophyll a
- Pheophytin
- Photosystem II
- Photophosphorylation
- Chlorophyll
- Photodissociation
- Photosynthetic reaction centre
- Photosystem
