Bacteriochlorophylls are a heterogeneous group of photosynthetic tetrapyrrole pigments that are synthesized by various anoxigenic phototrophic bacteria that carry out photosynthesis without oxygen evolution.
The spectral properties of bacteriochlorophylls in cells differ significantly from solutions, and are determined by non-covalent interactions of their molecules with proteins containing them, as well as with each other.
Content
- 1 Chemical structure of bacteriochlorophylls
- 2 Chemical properties
- 3 Biosynthesis
- 4 Distribution
The chemical structure of bacteriochlorophylls
Bacteriochlorophylls a , b and g are bacteriochlorins , that is, they contain a bacteriochlorin macrocycle with two reduced pyrrole rings (II and IV).
Bacteriochlorophylls c-f , like chlorophylls, have a chlorine macrocycle ring with a single fully reduced pyrrole ring IV. Unlike all other chlorophylls and bacteriochlorophylls, they lack the -COOCH 3 residue at position R 5 , which is characteristic of all other chlorophylls and bacteriochlorophylls. Each of these bacteriochlorophylls has several forms, differing in radicals R 3 and R 4 , as well as on esterifying alcohol R 5 [1] [2] .
| Title | Structure | R 1 | R 2 | R 3 | Communication C7-C8 | R 4 | R5 | R 6 | R 7 |
|---|---|---|---|---|---|---|---|---|---|
| Bacteriochlorophyll a | –CO – CH 3 | –CH 3 a | –CH 2 CH 3 | single | -CH 3 | -CO-O-CH 3 | -fitil geranyl geranyl | -H | |
| Bacteriochlorophyll b | -CO-CH 3 | -CH 3 a | = CH-CH 3 | single | –CH 3 | –CO – O – CH 3 | –Fitil | –H | |
| Bacteriochlorophyll c | –CHOH – CH 3 | –CH 3 | –C 2 H 5 b –C 3 H 7 –C 4 H 9 | double | –CH 3 –C 2 H 5 | –H | –Farnesil and others | –CH 3 | |
| Bacteriochlorophyll d | –CHOH – CH 3 | –CH 3 | –C 2 H 5 b –C 3 H 7 –C 4 H 9 | double | –CH 3 –C 2 H 5 | –H | –Farnesil and others | –H | |
| Bacteriochlorophyll e | –CHOH – CH 3 | –CHO | –C 2 H 5 b –C 3 H 7 –C 4 H 9 | double | –CH 3 –C 2 H 5 | –H | –Farnesil and others | –CH 3 | |
| Bacteriochlorophyll f | –CHOH – CH 3 | –CHO | –C 2 H 5 b –C 3 H 7 –C 4 H 9 | double | ––CH 3 –C 2 H 5 | –H | –Farnesil and others | –H | |
| Bacteriochlorophyll g | –CH = CH 2 | –CH 3 a | = CH-CH 2 | single | –CH 3 | –CO – O – CH 3 | Geranyl geranyl | –H |
Chemical Properties
Bacteriochlorophylls are unstable to light, acids and oxidizing agents. In polar solvents (for example, methanol) they easily undergo allomerization; in the presence of acids, they lose the central magnesium atom (pheophytinized) and / or the esterifying residue (phytol / farnesol / geranylgeriniol, etc.) [3] .
Bacteriochlorophylls b and g , having an ethylidene residue at C-8, in a slightly acidic medium are isomerized to form chlorins. Bacteriochlorophyll g is especially easily isomerized, resulting in chlorophyll a G [4] .
Under the action of oxygen in the molecules of bacteriochlorophylls, an oxidative rupture of the five-membered ring V occurs; subsequently, the formed acid residues at the c-13 and C-14 atoms can again close into a six-membered anhydride ring with the formation of bacteriopurpurines or purpurins [3] [5] .
Biosynthesis
A simplified scheme of the biosynthesis of bacteriochlorophyllides a, b and g , as well as (E, M) -bacteriochlorophyllides c-e [6] [7] , is shown in the figure.
It was previously assumed that the first stage of the biosynthesis of bacteriochlorophyll c-e, the formation of ring V without a carboxymethyl substituent at C13 2 , can occur even before the formation of 3,8-divinyl protochlorophyllide a [8] . This is currently considered unlikely [6] [9] .
The last stage of biosynthesis, the conversion of bacteriochlorophyllides to bacteriochlorophylls, is carried out using esterases encoded by the BchG genes in bacteriochlorophylls a, b and g, and BchK in chlorobium-chlorophylls. The synthesis of methylated forms of bacteriochlorophylls c-e also involves methylase C12 1 -carbon BchR and C8 2 -methylase BchQ. Apparently, any chlorophyllides with a hydroxymethyl residue at C3 serve as their substrates, i.e., methylation can occur at any stage after the formation of 8-ethyl-12-methyl-bacteriochlorophyllide d .
Distribution
The most common pigment of anoxigenic phototrophic bacteria is bacteriochlorophyll a . It is the predominant chlorine pigment in the reaction centers of most phototrophic proteobacteria, in all green sulfur bacteria (Chlorobiaceae) and filamentous anoxigenic phototrophs (Chloroflexia). In few phototrophic proteobacteria, bacteriochlorophyll a is completely replaced by bacteriochlorophyll b . Bacteriochlorophyll g was found only in one small group of bacteria, heliobacteria , by the number of species and distribution.
Bacteriochlorophylls c-f are present exclusively in chlorosomes, special photosynthetic antenna complexes found in all green sulfur bacteria (Chlorobiales) , some filamentous anoxigenic phototrophs (Chloroflexia), as well as in the recently discovered photoheterotrophic acidobacterium Chloracidobacterium] thermophilum .
| Pigment | Bacteria group | The maximum infrared absorption in vivo ( nm ) |
|---|---|---|
| Bacteriochlorophyll a | Purple bacteria (most), Chlorobiaceae, Chloroflexales and Chloracidobacterium thermophilum | 805-815, 830-890 |
| Bacteriochlorophyll b | Purple bacteria (some) | 835-850, 1020-1040 |
| Bacteriochlorophyll c | Chlorobiaceae (green strains) most Chloroflexia , Chloracidibacterium thermophilum | 745-755 |
| Bacteriochlorophyll d | green strains of Chlorobiaceae , Chloronema ( Chloroflexia ) | 705-740 |
| Bacteriochlorophyll e | brown strains of Chlorobiaceae | 719-726 |
| Bacteriochlorophyll f | some laboratory strains of Chlorobiaceae | ~ 705-707 |
| Bacteriochlorophyll g | Heliobacterium | 670-788 |
Notes
- ↑ Scheer, H. (2006). An overview of chlorophylls and bacteriochlorophylls: biochemistry, biophysics, functions and applications In: B. Grimm et al. (eds): Chlorophylls and Bacteriochlorophylls. Springer Netherlands. (pp. 1-26)
- ↑ Orf, GS, Blankenship, RE (2013). Chlorosome antenna complexes from green photosynthetic bacteria. Photosynthesis research , 116 (2-3), p. 15-331.
- ↑ 1 2 Keely, BJ (2006). Geochemistry of chlorophylls. In Chlorophylls and Bacteriochlorophylls (pp. 535-561). Springer Netherlands.
- ↑ Kobayashi, M., Hamano, T., Akiyama, M., Watanabe, T., Inoue, K., Oh-oka, H., Amesz J., Yamamura M., Kise, H. (1998). Light-independent isomerization of bacteriochlorophyll g to chlorophyll a catalyzed by weak acid in vitro. Analytica chimica acta , 365 (1), 199-203.
- ↑ Grin, MA, & Mironov, AF (2008). Synthetic and Natural Bacteriochlorins: Synthesis, Properties and Applications. In: Chemical Processes with Participation of Biological and Related Compounds: Biophysical and Chemical Aspects of Porphyrins, Pigments, Drugs, Biodegradable Polymers and Nanofibers , 5.
- ↑ 1 2 Liu, Z., & Bryant, DA (2011). Identification of a gene essential for the first committed step in the biosynthesis of bacteriochlorophyll c. Journal of Biological Chemistry , 286 (25), 22393-22402.
- ↑ Tsukatani Y., Yamamoto H., Harada J., Yoshitomi T., Nomata J., Kasahara M., Mizoguchi T., Fujita Y., Tamiaki H. (2013). An unexpectedly branched biosynthetic pathway for bacteriochlorophyll b capable of absorbing near-infrared light. Scientific reports , 3 .
- ↑ Frigaard, NU, Chew, AGM, Maresca, JA, & Bryant, DA (2006). Bacteriochlorophyll biosynthesis in green bacteria. In Chlorophylls and Bacteriochlorophylls (pp. 201-221). Springer Netherlands.
- ↑ Harada, J., Teramura, M., Mizoguchi, T., Tsukatani, Y., Yamamoto, K., & Tamiaki, H. (2015). Stereochemical conversion of C3 ‐ vinyl group to 1 ‐ hydroxyethyl group in bacteriochlorophyll c by the hydratases BchF and BchV: adaptation of green sulfur bacteria to limited ‐ light environments. Molecular microbiology , 98 (6), 1184-1198.
- ↑ Bryant, Donald A .; Costas, AM; Maresca, JA & Chew, AG (2007-07-27), " Candidatus Chloracidobacterium thermophilum: An Airobic Phototrophic Acidobacterium ", Science T. 317 (5837): 523-526, PMID 17656724 , doi : 10.1126 / science.1143236 , < http://www.sciencemag.org/cgi/content/abstract/317/5837/523 >