Bacteriochlorophyll

Bacteriochlorophylls (BChl) are photosynthetic pigments that occur in various phototrophic bacteria. They were discovered by C. B. van Niel in 1932. They are related to chlorophylls, which are the primary pigments in plants, algae, and cyanobacteria. Organisms that contain bacteriochlorophyll conduct photosynthesis to sustain their energy requirements, but do not produce oxygen as a byproduct. They use wavelengths of light not absorbed by plants or Cyanobacteria. Replacement of Mg2+ with protons gives bacteriophaeophytin (BPh), the phaeophytin form.
Structure.
Bacteriochlorophylls "a", "b", and "g" are bacteriochlorins, meaning their molecules have a bacteriochlorin macrocycle ring with two reduced pyrrole rings (B and D). Bacteriochlorophylls "c", "d", "e", and "f" are chlorins, meaning their molecules have a chlorin macrocycle ring with one reduced pyrrole ring (D).
Bacteriochlorophylls "c" to "f" occur in the form of closely related homologs with different alkyl groups attached to pyrrole rings B and C and are illustrated above in their simplest versions, esterified with the sesquiterpene alcohol farnesol. Bacteriochlorophyll "g" has a vinyl group in ring (A).
Biosynthesis.
There are a large number of known bacteriochlorophylls but all have features in common since the biosynthetic pathway involves chlorophyllide "a" as an intermediate. Isobacteriochlorins, in contrast, are biosynthesised from uroporphyrinogen III in a separate pathway that leads, for example, to siroheme, cofactor F430 and cobalamin.