Bacterio-chlorophyll

Figure 12.22 Schematic diagram showing the flow of excitation energy in the bacterial photosynthetic apparatus. The energy of a photon absorbed by LH2 spreads rapidly through the periplasmic ring of bacterio-chlorophyll molecules (green). Where two complexes touch in the membrane, the energy can be transmitted to an adjacent LH2 ring. From there it passes by the same mechanism to LHl and is finally transmitted to the special chlorophyll pair in the reaction center. (Adapted from W. Kiihlbrandf, Structure 3 521-525, 1995.)...

Electrochemical reduction has been studied intensively in the chlorophyll series due to the possibility to utilize the formed reduction products for the preparation of bacterio-chlorophylls.31c-d 41 For instance, methyl 3 -oxorhodochlorin-l5-acetate (4), a metal-free chlorin, can be electrochemically reduced to the corresponding chlorin 5 which is at the same oxidation level as a tetrahydroporphyrin. 

Figure 2 Molecular structures and IUPAC numbering scheme of organic cofactors occurring in photosynthetic reaction centres (bRC, PS I, PS II). (Bac-teriolpheophytin is the free base of (bacterio)chlorophyll plastoquinone (PQ) is found in PS If phylloquinone or vitamin K, ( VK,) in PS I many bacteria contain ubiquinone (UQ). Shown is also the amino acid tyrosine (Tyr, Y) that is redox active in PS II.

Tamiaki H, Shibata R and Mizoguchi T. The 17-propionate function of (bacterio)chlorophylls biological implication of their long esterifying chains in photosynthetic systems. Photochem. Photobiol. 2007 83 152-162. 

In Rp. viridis the four hemes in the cytochrome suhunit are connected to the cysteine residues in the protein via thioether bridges. The heme planes are parallel to the helical axes, but only the special bacterio-chlorophyll pair and the heme of the nearest cytochrome share the same axis. The distance between this cytochrome iron atom and either Mg atom of [BChl b]2 is 21 A. The iron-iron distance within each cytochrome pair is 14 A while that between two cytochrome pairs is 16 A. As expected, [BChl 6)2 extracts electrons from the nearest cytochrome. 

Figure 41 (a) The arrangement of the central cofactors of the Reaction Centre of Rh. viridis, according to an X-ray crystal structure analysis. SP, the special pair, is the primary electron donor in its excited state, BCh is an accessory bacterio-chlorophyll, and BPh, a bacterio-pheophtyin, is the primary electron acceptor [142-144], Photo-induced electron transfer from SP to BPh takes place in 3 ps [145-147], (b) A synthetic model of the natural system (128). [139, 140, 148] SP and BPh are mimicked respectively by a zinc(II) and a gold(III) porphyrin bridged by a dpp spacer. 

Figure 4. Left-. Structural model of the photosynthetic reaction center of Rps. viridis from crystal structure data. Right. Arrangement of the special pair (dark gray), accessory bacterio-chlorophyll (black), and the bacteriopheophytin (light gray) pigments.

Fig. 3.19 The results of the SVD and global-fitting analysis of time-resolved EPR data matrix at 100 K. A three-component analysis (A) incorporated the special-pair bacterio-chlorophylls in the T state (3P) as well as two (3Car(l) and 3Car(ll)) triplet species of...

Grimm B, Porra R, Rudiger W, Scheer H (eds.) (2006) Chlorophylls and Bacterio-chlorophylls Biochemistry, Biophysics, Functions and Applications. Springer, Dordrecht, The Netherlands... 

Wiemken V and Bachofen R (1984) Probing the smallest functional unit of the reaction center of Rhodospirillum rubrum G-9 with proteinoses. FEBS Lett 166 155-159 Williams JC, Alden RG, Murchison HA, Peloquin JM, Woodbury NW and Allen IP (1992) Effects of mutations near the bacteriochlorophylls in reaction centers from Rhodobacter sphaeroides. Biochemistry 31 11029-11037 Yeates TO, Komiya H, Chirino A, Rees DC, Allen IP and Feher G (1988) Structure of the reaction center from Rhodobacter sphaeroides R-26 and 2.4.1 Protein-cofactor bacterio-chlorophyll bacteriopheophytin and carotenoid interactions. Proc Natl Acad Sci USA 85 7993-7997 Zinth W, Knapp EW, Fischer SF, Kaiser W, Deisenhofer J and Michel H (1985) Correlation of structural and spectroscopic properties of a photo synthetic reaction center. Chem Phys Lett 119 1 ... 

Stmck A, Cmiel E, Katheder 1 and Scheer H (1990b) Modified reaction centers from Rb. sphaeroides R-26 2 Bacterio-chlorophylls with modified C-3 substituents at sites and Bq. FEBS Lett 268 180-184... 

Krasnovsky Jr, AA, Cheng P, Blankenship RE, Moore TA and Gust D (1993) The photophysics of monomeric bacterio-chlorophylls c and d and their derivatives Properties of the triplet state and singlet oxygen photogeneration and quenching. Photochem Photobiol 57 324-330... 

Krueger BP, Scholes GD, Jimenez R, and Fleming GR (1998) Electronic excitation transfer from carotenoid to bacterio-chlorophyl in the purple bacterium Rhodopseudomonas acidophila. J Phys Chem, 102 2284-2292... 

Figure 10,1. Key types of vanadium complexes in petroleum (a) porphyrins, (b) mixed ligands such as N2O2 type, the -ketimines, (c) pseudoaromatic pheophorbides such as a bacterio-chlorophyll (the outer conjugation is interrupted, but still belong to the diaza-ld-annulene system), and (d) highly aromatic porphins such as the dehydrogenated product of m-a-naphylporphyrin, which was identified in Nonesuch shale. Type (a) is found in all petroleum. Types (b), (c) and (d) are commonly referred to as the nonporphyrin type of vanadium...

---