Bacteriochlorophyll e : structure and stereochemistry of a new type of chlorophyll from Chlorobiaceae

Abstract

A so far unknown chlorophyll has been isolated from several strains of brown-coloured chlorobacteria and has been designated bacteriochlorophyll e . Comparison of the physical and chemical properties of the new chlorophyll with those of bacteriochlorophylls c and d ( Chlorbium chlorophylls) allows one to deduce its structural formula. The stereochemistry of the hydroxyethyl side chain of bacteriochlorophylls c, d and e can be determined by a modified Horeau analysis of these pigments, and the results thus obtained are in agreement with those derived from oxidative degradation experiments. The latter method allows one furthermore to prove the structure of bacteriochlorophylls c and d proposed by Holt, and to establish the absolute configuration at carbon atoms 7 and 8. The presence of a δ-methylsubstituent in bacteriochlorophylls c and e is unambiguously demonstrated by nuclear magnetic resonance.

Chlorophyll Biosynthesis in Bacteria: The Origins of Structural and Functional Diversity

“…Until very recently, the branching point for the biosynthetic pathway leading to BChl c from that for Chl a and BChl a in C. tepidum was unknown. Because of the existence of multiple large subunits of Mgchelatase, the branch point leading to BChl c had initially been suggested to occur at the level of Proto-IX (13,21). An alternative possibility, now excluded by mutational analyses, is that a BChl c-specific oxidative cyclase was responsible for the formation of the isocyclic E-ring and the oxidative decarboxylation at C-13 (22).…”

“…are the only prokaryotes that can produce Chl b (or divinyl-Chl b) as do higher plants (17,61). BChl e and BChl c only differ in that the former has a formyl group at the C-7 position (Figure 2z) (13). The addition of this formyl group causes a red-shift of 33 nm in the Soret region and a blue-shift of 15 nm of the Q y peaks of Chl b with respect to the maxima of Chl a.…”

Chlorophyll Organization and Function in Green Photosynthetic Bacteria

“…For BChl c from C ' auruntiucus R , = R, = R, = methyl, R, = ethyl, and R, = stearyl (major), phytyl (minor), geranylgeraniol (minor), cetyl (minor) or oleyl (minor) (161,162). In green sulfur bacteria BChl c is a mixture of several homologs in which R, = R, = methyl, R, = ethyl, n-propyl or isobutyl, R, = ethyl or methyl and R, = farnesyl (91%), phytyl (3%), cetyl (3%) or tetrahydrogeranylgeranyl (2%) (169)(170)(171). Bacteriochlorophyll d is also a mixture in which R, = H, R, = methyl, R3 = ethyl, n-propyl, isobutyl or neopentyl, R, = methyl or ethyl and R, = farnesyl (major) (169,170).…”

wPMLG‐5 Spectroscopy of Self‐Aggregated BChl e in Natural Chlorosomes of Chlorobaculum Limnaeum

“…[24,25] It has a similar structure to BChl c and is the only BChl with a formyl group at carbon C7, instead of a methyl group (Figure 1). Similarly to other BChls that are found in nature, BChl e exists as different homologs, which vary in their chirality at C3 1 (R/S-epimers), in their C8 and C12 methylated substituents, and in the esterifying alcohol chains at C17.…”