Bacteriopheophytin g : Properties and some speculations on a possible primary role for bacteriochlorophylls b and g in the biosynthesis of chlorophylls

Abstract

Bacteriopheophytin g and small amounts of bacteriochlorophyll g have been obtained in high purity from the recently discovered photosynthetic bacterium Heliobacterium chlorum . Preparative methods and precautions in handling these sensitive compounds are described. The compounds have been characterized by californium-252 plasma desorption mass spectrometry, HPLC, visible absorption, and electron spin resonance spectroscopy. Our results agree with the structure of bacteriochlorophyll g advanced by H. Brockmann and A. Lipinski [(1983) Arch. Microbiol . 136, 17-19], with the exception that we find the esterifying alcohol to be farnesol and not geranylgeraniol as originally suggested. Zero field splitting parameters of triplet state bacteriopheophytin g and the ESR properties of the cation free radical of bacteriochlorophyll g are reported. The photoisomerization of the subject compounds has been studied. Bacteriopheophytin g undergoes photo-isomerization in white light to pheophytin a with a half-time of ≈42 min. We suggest that all of the chlorophylls are biosynthesized from a common intermediate containing an ethylidine group, [unk]CH—CH 3 , such as is present in bacteriochlorophylls b and g .

The derivation of the formyl‐group oxygen of chlorophyll b in higher plants from molecular oxygen

“…Hydratases directed at the C7 exocyclic double bond lead to the formation of a 7-hydroxymethyl derivative and eventually lead to the formation of Chl b (see Schemes B1 and B2). Exocyclic double bonds are known in other chlorophylls, such as bacteriochlorophyll b [15] and g [16], which possess an ethylidene group at C8 : such double bonds have been postulated to play an important role in the biosynthesis of other chlorophylls [16]. If either hydratase scheme (B1 or B2) operates, the 7-formyl oxygen would arise from water and greening in the presence of H,"O would lead to an increase of 2Da in the molecular mass of Chl b: the molecular mass of Chl a would be unaffected.…”

Mass Spectrometry of Chlorophylls from Phototrophic Prokaryotes

“…Bacteriochlorophyll g, like bacteriochlorophylls a and b, has a bacteriochlorin π-system with single bonds at C-7-C-8 and C-17-C-18. Bacteriochlorophyll and bacteriophaeophytin g have been analysed by heavy ion desorption mass spectrometry ( 252 Cf-PDMS; [75], a time of flight technique in which molecular ions of the sample are created by impact of fission fragment ions resulting from the spontaneous fission of 252 Cf. Under these conditions, average molecular ions at m/z 819 and 797 were observed for bacteriochlorophyll and bacteriophaeophytin g, respectively [75], differing in 22 Da, the expected mass difference between magnesium-chelated and unchelated (bacterio)chlorophylls.…”

“…Bacteriochlorophyll and bacteriophaeophytin g have been analysed by heavy ion desorption mass spectrometry ( 252 Cf-PDMS; [75], a time of flight technique in which molecular ions of the sample are created by impact of fission fragment ions resulting from the spontaneous fission of 252 Cf. Under these conditions, average molecular ions at m/z 819 and 797 were observed for bacteriochlorophyll and bacteriophaeophytin g, respectively [75], differing in 22 Da, the expected mass difference between magnesium-chelated and unchelated (bacterio)chlorophylls. Ions occurring at [M-204] + were also observed in the mass spectra, indicating bacteriochlorophyll g was esterified by farnesol, and not geranyl geraniol as previously suggested [74].…”

An Overview of Chlorophylls and Bacteriochlorophylls: Biochemistry, Biophysics, Functions and Applications

“…In some purple bacteria, it is replaced by the structurally related BChl b, carrying an 8-ethylidene instead of the 8-ethyl group present in BChl a (Scheer et al, 1974;Steiner et al, 1981). BChl g is found in the strictly anaerobic Gram-positive heliobacteria, both as a light-harvesting and as an electron transfer pigment in the functionally integrated type I-RC complex (Michalski et al, 1987;Neerken and Amesz, 2001;Chapter 4, Kobayashi et al).…”