Light gathering pigments

One of the important properties of porphyrins is that they complex with divalent metals, the pyrrole nitrogens being ideally spaced to allow this. Of vital importance to life processes are the porphyrin derivatives chlorophyll and haem. Chlorophyll (actually a mixture of structurally similar porphyrins chlorophyll a is shown) contains magnesium, and is, of course, the light-gathering pigment in plants that permits photosynthesis. 

Key LGP, light-gathering pigments (accessory pigments and chlorophylls other than P700 and P690) PQ, plasto-quinone CYT, cytochrome PC, plastocyanin FD, ferredoxin. 

Figure 12.1. Schematic diagram of a photosynthesis reaction center. Light is absorbed by pigments in the light-gathering antenna and absorbed energy is transferred to a photochemically active site P, where it is utilized to initiate photosynthetic reactions.

See also Light Absorbing Pigments, Light Gathering Structures... 

It is now known that in the bacterial systems the donor is a pair of chlorophyll molecules, the special pair", P, and the initial acceptors is either another chlorophyll molecule, an auxiliary chlorophyll B, or a bacteriopheophytin, H, a chlorophyll molecule in which the central magnesium ion has been replaced by a pair of protons. Although many pigments are present acting as antenna molecules to gather the light, additional chlorophylls are most common. How can the same molecule have such different roles In spite of the fact that the antenna and the RC pair molecules are the same, light is transferred from the antenna to the RC with unit efficiency. 

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