Bacteriochlorophyll Explained

Bacteriochlorophylls (BChl) are photosynthetic pigments that occur in various phototrophic bacteria. They were discovered by C. B. van Niel in 1932.[1] 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 the process is anoxygenic and does not produce oxygen as a byproduct. They use wavelengths of light not absorbed by plants or cyanobacteria. Replacement of with protons gives bacteriophaeophytin (BPh), the phaeophytin form.

List of major bacteriochlorophylls! Pigment! Taxa! in vivo infrared absorption maximum (nm)
BChl aPurple bacteria, Heliobacteria, Green Sulfur Bacteria, Chloroflexota, Chloracidobacterium thermophilum805, 830–890
BChl b835–850, 1020–1040
BChl cGreen sulfur bacteria, Chloroflexota, C. thermophilum, C. tepidum745–755
BChl dGreen sulfur bacteria705–740
BChl eGreen sulfur bacteria719–726
BChl f(Discovered by mutation of BChl e synthesis by analogy to BChl c/d. Not evolutionarily favorable.)[2] 700–710
BChl gHeliobacteria670, 788

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).[3]

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.[4] Most of the variation occurs in the 8 and 12 positions and can be attributed to methyltransferase variation.[5] BChl cS is a term for 8-ethyl,12-methyl homolog of BChl c.[6]

Bacteriochlorophyll g has a vinyl group in ring (A), at position 8.[7]

Biosynthesis

There are a large number of known bacteriochlorophylls[3] [8] but all have features in common since the biosynthetic pathway involves chlorophyllide a (Chlide a) as an intermediate.[9]

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 bound between C7 and C8, which is performed by Chlorophyllide a reductase (COR).[8]

Isobacteriochlorins, in contrast, are biosynthesised from uroporphyrinogen III in a separate pathway that leads, for example, to siroheme, cofactor F430 and cobalamin. The common intermediate is sirohydrochlorin.[10]

Notes and References

  1. 10.1007/BF00454965 . On the morphology and physiology of the purple and green sulphur bacteria . 1932 . Niel . C. B. . 19597530 . Archiv für Mikrobiologie . 3 . 1–112 .
  2. Vogl . Kajetan. Bacteriochlorophyll f: properties of chlorosomes containing the "forbidden chlorophyll". Front. Microbiol.. 3 . article 298, pages 1–12 . 2012-08-10. 10.3389/fmicb.2012.00298. 22908012. Tank. M. Orf. GS. Blankenship. RE. Bryant. DA. vanc. 1 . 3415949. free.
  3. Book: 10.1007/0-306-47954-0_8 . Biosynthesis and Structures of the Bacteriochlorophylls . Anoxygenic Photosynthetic Bacteria . Advances in Photosynthesis and Respiration . 2004 . Senge . Mathias O. . Smith . Kevin M. . 2 . 137–151 . 0-7923-3681-X .
  4. 10.1002/cptc.201700164 . In Vivo Energy Transfer from Bacteriochlorophyll c, d, e, or f to Bacteriochlorophyll a in Wild-Type and Mutant Cells of the Green Sulfur Bacterium Chlorobaculum limnaeum . 2018 . Harada . Jiro . Shibata . Yutaka . Teramura . Misato . Mizoguchi . Tadashi . Kinoshita . Yusuke . Yamamoto . Ken . Tamiaki . Hitoshi . ChemPhotoChem . 2 . 3 . 190–195 .
  5. Gomez Maqueo Chew . A . Frigaard . NU . Bryant . DA . Bacteriochlorophyllide c C-8(2) and C-12(1) methyltransferases are essential for adaptation to low light in Chlorobaculum tepidum. . Journal of Bacteriology . September 2007 . 189 . 17 . 6176–84 . 10.1128/JB.00519-07 . 17586634. 1951906 .
  6. Gloe . A . Risch . N . Bacteriochlorophyll cs, a new bacteriochlorophyll from Chloroflexus aurantiacus. . Archives of Microbiology . 1 August 1978 . 118 . 2 . 153–6 . 10.1007/BF00415723 . 697505. 20011765 .
  7. 10.1016/j.bbabio.2013.06.007 . Completion of biosynthetic pathways for bacteriochlorophyll g in Heliobacterium modesticaldum: The C8-ethylidene group formation . 2013 . Tsukatani . Yusuke . Yamamoto . Haruki . Mizoguchi . Tadashi . Fujita . Yuichi . Tamiaki . Hitoshi . Biochimica et Biophysica Acta (BBA) - Bioenergetics . 1827 . 10 . 1200–1204 . 23820336 . free .
  8. 10.1146/annurev.micro.61.080706.093242 . Chlorophyll Biosynthesis in Bacteria: The Origins of Structural and Functional Diversity . 2007 . Chew . Aline Gomez Maqueo . Bryant . Donald A. . Annual Review of Microbiology . 61 . 113–129 . 17506685 .
  9. Biosynthesis of chlorophylls from protoporphyrin IX . Willows . Robert D. . Natural Product Reports . 2003 . 20 . 6 . 327–341 . 10.1039/B110549N . 12828371.
  10. 10.1039/B002635M . Tetrapyrroles: The pigments of life: A Millennium review . 2000 . Battersby . Alan R. . Natural Product Reports . 17 . 6 . 507–526 . 11152419 .

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