Bacteriochlorophylls (BChl) are

photosynthetic pigment A photosynthetic pigment (accessory pigment; chloroplast pigment; antenna pigment) is a pigment that is present in chloroplasts or photosynthetic bacteria and captures the light energy necessary for photosynthesis. List of photosynthetic pigmen ...

s that occur in various

phototroph Phototrophs () are organisms that carry out photon capture to produce complex organic compounds (e.g. carbohydrates) and acquire energy. They use the energy from light to carry out various cellular metabolic processes. It is a list of common m ...

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

. They were discovered by C. B. van Niel in 1932. They are related to

chlorophyll Chlorophyll is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. Its name is derived from the Greek words (, "pale green") and (, "leaf"). Chlorophyll allows plants to absorb energy ...

s, which are the primary pigments in

plant Plants are the eukaryotes that form the Kingdom (biology), kingdom Plantae; they are predominantly Photosynthesis, photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with c ...

alga Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular microalgae, suc ...

e, and

cyanobacteria Cyanobacteria ( ) are a group of autotrophic gram-negative bacteria that can obtain biological energy via oxygenic photosynthesis. The name "cyanobacteria" () refers to their bluish green (cyan) color, which forms the basis of cyanobacteri ...

. Organisms that contain bacteriochlorophyll conduct

photosynthesis Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabo ...

to sustain their energy requirements, but the process is anoxygenic and does not produce

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

as a

byproduct A by-product or byproduct is a secondary product derived from a production process, manufacturing process or chemical reaction; it is not the primary product or service being produced. A by-product can be useful and marketable or it can be cons ...

. They use wavelengths of light not absorbed by plants or

. Replacement of with protons gives bacteriophaeophytin (BPh), the phaeophytin form. BacterioChlorophyll a.svg, bacteriochlorophyll ''a'' BacterioChlorophyll b.svg, bacteriochlorophyll ''b'' BacterioChlorophyll c.svg, bacteriochlorophyll ''c'' BacterioChlorophyll d.svg, bacteriochlorophyll ''d'' BacterioChlorophyll e.svg, bacteriochlorophyll ''e'' Bacteriochlorophyll f.svg, bacteriochlorophyll ''f'' BacterioChlorophyll g.svg, bacteriochlorophyll ''g''

Structure

Bacteriochlorophylls ''a'', ''b'', and ''g'' are bacteriochlorins, meaning their molecules have a bacteriochlorin

macrocycle Macrocycles are often described as molecules and ions containing a ring of twelve or more atoms. Classical examples include the crown ethers, calixarenes, porphyrins, and cyclodextrins. Macrocycles describe a large, mature area of chemistry. ...

ring with two reduced

pyrrole Pyrrole is a heterocyclic, aromatic, organic compound, a five-membered ring with the formula . It is a colorless volatile liquid that darkens readily upon exposure to air. Substituted derivatives are also called pyrroles, e.g., ''N''-methylpyrrol ...

rings (B and D). Bacteriochlorophylls ''c'', ''d'', ''e'', and ''f'' are

chlorin In organic chemistry, chlorins are tetrapyrrole pigments that are partially hydrogenation, hydrogenated porphyrins. The parent chlorin is an unstable compound which undergoes air oxidation to porphine. The name chlorin derives from chlorophyll. ...

s, meaning their molecules have a chlorin

ring with one reduced pyrrole ring (D). Bacteriochlorophylls ''c'' to ''f'' occur in the form of closely related homologs with different

alkyl group In organic chemistry, an alkyl group is an alkane missing one hydrogen. The term ''alkyl'' is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of . A cycloalkyl group is derived from a cy ...

s attached to pyrrole rings B and C and are illustrated above in their simplest versions,

ester In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...

ified with the

sesquiterpene Sesquiterpenes are a class of terpenes that consist of three isoprene units and often have the molecular formula C15H24. Like monoterpenes, sesquiterpenes may be cyclic or contain rings, including many combinations. Biochemical modifications s ...

alcohol farnesol. Most of the variation occurs in the 8 and 12 positions and can be attributed to methyltransferase variation. BChl ''c_S'' is a term for 8-ethyl,12-methyl homolog of BChl ''c''. Bacteriochlorophyll ''g'' has a vinyl group in ring (A), at position 8.

Biosynthesis

There are a large number of known bacteriochlorophylls but all have features in common since the biosynthetic pathway involves chlorophyllide ''a'' (Chlide ''a'') as an intermediate. Chlorin-cored BChls (''c'' to ''f'') are produced by a series of enzymatic modifications on the sidechain of Chlide ''a'', much like how Chl ''b'', ''d'', ''e'' are made. The bacteriochlorin-cored BChls ''a'', ''b'', ''g'' require a unique step to reduce the double bond between C7 and C8, which is performed by chlorophyllide ''a'' reductase (COR). Isobacteriochlorins, in contrast, are biosynthesised from uroporphyrinogen III in a separate pathway that leads, for example, to siroheme, cofactor F₄₃₀ and

cobalamin Vitamin B12, also known as cobalamin, is a water-soluble vitamin involved in metabolism. One of eight B vitamins, it serves as a vital cofactor (biochemistry), cofactor in DNA synthesis and both fatty acid metabolism, fatty acid and amino a ...

. The common intermediate is sirohydrochlorin.

References

{{photolithotrophic bacteria Photosynthetic pigments Tetrapyrroles de:Chlorophylle#Chemische Struktur bei anoxygenen Phototrophen: Bakteriochlorophylle (Bchl)