Chlorophyllous pigments are essential for photosynthesis. Bacteriochlorophyll (BChl) b has the characteristic C8-ethylidene group and therefore is the sole naturally occurring pigment having an absorption maximum at near-infrared light wavelength. Here we report that chlorophyllide a oxidoreductase (COR), a nitrogenase-like enzyme, showed distinct substrate recognition and catalytic reaction between BChl a- and b-producing proteobacteria. COR from BChl b-producing Blastochloris viridis synthesized the C8-ethylidene group from 8-vinyl-chlorophyllide a. In contrast, despite the highly conserved primary structures, COR from BChl a-producing Rhodobacter capsulatus catalyzes the C8-vinyl reduction as well as the previously known reaction of the C7 = C8 double bond reduction on 8-vinyl-chlorophyllide a. The present data indicate that the plasticity of the nitrogenase-like enzyme caused the branched pathways of BChls a and b biosynthesis, ultimately leading to ecologically different niches of BChl a- and b-based photosynthesis differentiated by more than 150 nm wavelength.
Five Citrus-type crude drugs (40 samples) were classified using liquid chromatography−mass spectrometry (LC-MS)-based metabolomics. The following six flavonoid derivatives were identified as contributors from the loading plots of multivariate analysis: naringin (1), neohesperidin (2), neoeriocitrin (3), narirutin (9), hesperidin (10), and 3,5,6,7,8,3′,4′heptamethoxyflavone (12). Three coumarin derivatives, namely, meranzin (6), meranzin hydrate (7), and meranzin glucoside (8), were also identified as contributors. Furthermore, compared with our previous studies on proton ( 1 H) and 13 C NMR spectroscopy-based metabolomics, the present study revealed that the Citrus-type crude drugs were distinguished with the same pattern; however, the contributors differed between the 1 H and 13 C NMR spectroscopy-based metabolomics. The high dynamic range of NMR spectroscopy provided broad coverage of the metabolomes including the primary and secondary metabolites. However, LC-MS appeared to be superior in detecting secondary metabolites with high sensitivity, some of which occurred in quantities that were undetectable using NMR spectroscopy.
Glycolipids were isolated from extramembraneous light-harvesting complexes, called “chlorosomes,” in a thermophilic green photosynthetic bacterium Chlorobium tepidum. The lipids were first characterized in terms of their precise structures of both hydrophilic (saccharides) and hydrophobic (fatty acids) moieties by means of 1H and 13C NMR spectroscopy as well as high-performance liquid chromatography coupled with an evaporative light-scattering detector and an electron spray ionization mass spectrometer. The results clearly demonstrated that glycolipids having a disaccharide group, rhamnosylgalactosyldiacylglycerides, were the majority in the total glycolipid component of the chlorosomes, in addition to the second major glycolipids with a monosaccharide group, monogalactosyldiacylglycerides, which had been believed to be predominant before the report by Miller and her co-workers (Photosynth. Res.2008, 95, 191–196). We also found that these glycolipids had methylene-bridged palmitoleyl (=(Z)-9-hexadecenoyl) (17:1) and palmitoyl groups (16:0) as their predominant acyl chains on the glycerol moiety. By using enzymatically site-specific hydrolysis of the acyl chain at the sn-1 position on the glycerol, the modified palmitoleyl group was determined to be esterified at the sn-1 position. These unique glycolipids might play an important role in maintaining fluidization of chlorosomal envelopes and achieving thermal stability of chlorosomes at 45 °C.
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