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Bacteriochlorophyll

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 Mg2+ with protons gives bacteriophaeophytin (BPh), the phaeophytin form.

Bacteriochlorophyll a
Names
IUPAC name
[methyl (3S,4S,13R,14R,21R)-9-acetyl-14-ethyl-4,8,13,18-tetramethyl-20-oxo-3-(3-oxo-3-([(2E,7R,11R)-3,7,11,15-tetramethylhexadec-2-en-1-yl]oxy)propyl)-13,14-dihydrophorbine-21-carboxylatato(2−)-kappa4N23,N24,N25,N26]magnesium
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
KEGG
  • InChI=1S/C55H75N4O6.Mg/c1-13-39-34(7)41-29-46-48(38(11)60)36(9)43(57-46)27-42-35(8)40(52(58-42)50-51(55(63)64-12)54(62)49-37(10)44(59-53(49)50)28-45(39)56-41)23-24-47(61)65-26-25-33(6)22-16-21-32(5)20-15-19-31(4)18-14-17-30(2)3;/h25,27-32,34-35,39-40,51H,13-24,26H2,1-12H3,(H-,56,57,58,59,60,62);/q-1;+2/p-1/b33-25+;/t31-,32-,34-,35+,39-,40+,51-;/m1./s1 checkY[EBI]
    Key: DSJXIQQMORJERS-AGGZHOMASA-M
  • CC[C@@H]1[C@@H](C)C2=N/C/1=C\c3c(C)c4C(=O)[C@H](C(=O)OC)\C\5=C/6\N=C(\C=C\7/N([Mg]n3c45)\C(=C/2)\C(=C7C)C(=O)C)[C@@H](C)[C@@H]6CCC(=O)OC\C=C(/C)\CCC[C@H](C)CCC[C@H](C)CCCC(C)C
Properties
MgC55H74N4O6
Molar mass 911.524 g·mol−1
Appearance Light green to blue-green powder
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
List of major bacteriochlorophylls
Pigment Taxa in vivo infrared absorption maximum (nm)
BChl a Purple bacteria, Heliobacteria, Green Sulfur Bacteria, Chloroflexota, Chloracidobacterium thermophilum[2] 805, 830–890
BChl b Purple bacteria 835–850, 1020–1040
BChl c Green sulfur bacteria, Chloroflexota, C. thermophilum,[2] C. tepidum 745–755
BChl d Green sulfur bacteria 705–740
BChl e Green sulfur bacteria 719–726
BChl f (Discovered by mutation of BChl e synthesis by analogy to BChl c/d. Not evolutionarily favorable.)[3] 700–710
BChl g Heliobacteria 670, 788
  • Structures of major bacteriochlorophylls
  • bacteriochlorophyll a
    bacteriochlorophyll a
  • bacteriochlorophyll b
    bacteriochlorophyll b
  • bacteriochlorophyll c
    bacteriochlorophyll c
  • bacteriochlorophyll d
    bacteriochlorophyll d
  • bacteriochlorophyll e
    bacteriochlorophyll e
  • bacteriochlorophyll f
    bacteriochlorophyll f
  • bacteriochlorophyll g
    bacteriochlorophyll g

Structure

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Chemical structures comparing porphin, chlorin, bacteriochlorin, and isobacteriochlorin. Note relocation of C=C double bond between the two bacteriochlorin isomers. There are two π electrons (symbolized by π e−) for every double bond in the macrocycle.

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).[4]

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.[5] Most of the variation occurs in the 8 and 12 positions and can be attributed to methyltransferase variation.[6] BChl cS is a term for 8-ethyl,12-methyl homolog of BChl c.[7]

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

Biosynthesis

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The common biosynthetic precursor for bacteriochlorophylls is chlorophyllide a

There are a large number of known bacteriochlorophylls[4][9] but all have features in common since the biosynthetic pathway involves chlorophyllide a (Chlide a) as an intermediate.[10]

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).[9]

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.[11]

References

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  1. ^ Niel, C. B. (1932). "On the morphology and physiology of the purple and green sulphur bacteria". Archiv für Mikrobiologie. 3: 1–112. doi:10.1007/BF00454965. S2CID 19597530.
  2. ^ a b Bryant DA, et al. (2007-07-27), "Candidatus Chloracidobacterium thermophilum: An Aerobic Phototrophic Acidobacterium", Science, 317 (5837): 523–526, Bibcode:2007Sci...317..523B, doi:10.1126/science.1143236, PMID 17656724, S2CID 20419870
  3. ^ Vogl K, et al. (2012-08-10). "Bacteriochlorophyll f: properties of chlorosomes containing the "forbidden chlorophyll"". Front. Microbiol. 3: article 298, pages 1–12. doi:10.3389/fmicb.2012.00298. PMC 3415949. PMID 22908012.
  4. ^ a b Senge, Mathias O.; Smith, Kevin M. (2004). "Biosynthesis and Structures of the Bacteriochlorophylls". Anoxygenic Photosynthetic Bacteria. Advances in Photosynthesis and Respiration. Vol. 2. pp. 137–151. doi:10.1007/0-306-47954-0_8. ISBN 0-7923-3681-X.
  5. ^ Harada, Jiro; Shibata, Yutaka; Teramura, Misato; Mizoguchi, Tadashi; Kinoshita, Yusuke; Yamamoto, Ken; Tamiaki, Hitoshi (2018). "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". ChemPhotoChem. 2 (3): 190–195. doi:10.1002/cptc.201700164.
  6. ^ Gomez Maqueo Chew, A; Frigaard, NU; Bryant, DA (September 2007). "Bacteriochlorophyllide c C-8(2) and C-12(1) methyltransferases are essential for adaptation to low light in Chlorobaculum tepidum". Journal of Bacteriology. 189 (17): 6176–84. doi:10.1128/JB.00519-07. PMC 1951906. PMID 17586634.
  7. ^ Gloe, A; Risch, N (1 August 1978). "Bacteriochlorophyll cs, a new bacteriochlorophyll from Chloroflexus aurantiacus". Archives of Microbiology. 118 (2): 153–6. doi:10.1007/BF00415723. PMID 697505. S2CID 20011765.
  8. ^ Tsukatani, Yusuke; Yamamoto, Haruki; Mizoguchi, Tadashi; Fujita, Yuichi; Tamiaki, Hitoshi (2013). "Completion of biosynthetic pathways for bacteriochlorophyll g in Heliobacterium modesticaldum: The C8-ethylidene group formation". Biochimica et Biophysica Acta (BBA) - Bioenergetics. 1827 (10): 1200–1204. doi:10.1016/j.bbabio.2013.06.007. PMID 23820336.
  9. ^ a b Chew, Aline Gomez Maqueo; Bryant, Donald A. (2007). "Chlorophyll Biosynthesis in Bacteria: The Origins of Structural and Functional Diversity". Annual Review of Microbiology. 61: 113–129. doi:10.1146/annurev.micro.61.080706.093242. PMID 17506685.
  10. ^ Willows, Robert D. (2003). "Biosynthesis of chlorophylls from protoporphyrin IX". Natural Product Reports. 20 (6): 327–341. doi:10.1039/B110549N. PMID 12828371.
  11. ^ Battersby, Alan R. (2000). "Tetrapyrroles: The pigments of life: A Millennium review". Natural Product Reports. 17 (6): 507–526. doi:10.1039/B002635M. PMID 11152419.
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