title: An unexpectedly branched biosynthetic pathway for bacteriochlorophyll b capable of absorbing near-infrared light.
abstract: 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.
authors: Graduate School of Life Sciences, Ritsumeikan University, Shiga 525-8577, Japan. yusuke-t@fc.ritsumei.ac.jp
authors: Yusuke
authors: Y
authors: Tsukatani
authors: Haruki
authors: H
authors: Yamamoto
authors: Jiro
authors: J
authors: Harada
authors: Taichi
authors: T
authors: Yoshitomi
authors: Jiro
authors: J
authors: Nomata
authors: Masahiro
authors: M
authors: Kasahara
authors: Tadashi
authors: T
authors: Mizoguchi
authors: Yuichi
authors: Y
authors: Fujita
authors: Hitoshi
authors: H
authors: Tamiaki
mesh_terms: D020561:Alphaproteobacteria / Q000201:enzymology / Q000378:metabolism; D025541:Bacteriochlorophyll A / Q000737:chemistry / Q000378:metabolism; D001429:Bacteriochlorophylls / Q000737:chemistry / Q000378:metabolism*; D053898:Biosynthetic Pathways; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics; D016354:Rhodobacter capsulatus / Q000201:enzymology / Q000378:metabolism; D019265:Spectroscopy, Near-Infrared; D013379:Substrate Specificity
chemical_list: D025541:Bacteriochlorophyll A; D001429:Bacteriochlorophylls; D011994:Recombinant Proteins; C107900:bacteriochlorophyll b; D044925:Oxidoreductases Acting on CH-CH Group Donors; C511363:chlorophyllide a reductase, Rhodobacter capsulatus
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