title: Characterization of chlorophyll pigments in the mutant lacking 8-vinyl reductase of green photosynthetic bacterium Chlorobaculum tepidum.
abstract: The mutant lacking the enzyme BciA (renamed CT1063), which catalyzed reduction of the 8-vinyl group of a porphyrinoid-type 3,8-divinyl-(proto)chlorophyllide-a [DV-(P)Chlide-a] in the green sulfur bacterium Chlorobaculum (Cba.) tepidum, was reconstructed on the basis of the previous study reported by Chew and Bryant [J. Biol. Chem.2007, 282, 2967-2975]. Cba. tepidum biosynthesizes the following three different types of chlorophylls (Chls) through their common precursory DV-(P)Chlide-a as its photosynthetically active pigments: bacteriochlorophyll(BChl)-c and Chl-a with the partially reduced 17,18-trans-dihydroporphyrin and BChl-a with the further reduced 7,8-trans-17,18-trans-tetrahydroporphyrin. The structures of Chls thus produced were characterized in detail by various spectroscopic techniques. In the mutant, both BChl-c and Chl-a possessing the alkyl group at the 8-position were exclusively replaced by their 8-vinylated derivatives, whereas BChl-a possessed the original 8-ethyl group. The present observations were inconsistent with the previous report. However, it was apparently confirmed that the enzyme BciA was responsible for the reduction of DV-(P)Chlide-a to produce BChl-c and Chl-a. Noteworthily, exclusive accumulation of the reduced (8-ethylated) form of BChl-a, not its 8-vinylated derivative, in the mutant indicates the presence of another enzyme catalyzing the 8-vinyl reduction as yet unidentified or any other reduction mechanism using a known enzyme to yield BChl-a.
authors.affiliation: Graduate School of Life Sciences, Ritsumeikan University, Kusatsu, Shiga, Japan.
authors.forename: Tadashi
authors.initials: T
authors.lastname: Mizoguchi
authors.forename: Jiro
authors.initials: J
authors.lastname: Harada
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Tamiaki
mesh_terms: D001429:Bacteriochlorophylls / Q000737:chemistry* / Q000378:metabolism; D019414:Chlorobi / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics* / Q000378:metabolism; D017353:Gene Deletion; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000235:genetics*
chemical_list: D001429:Bacteriochlorophylls; D010088:Oxidoreductases