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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.

Citation

Yusuke Tsukatani, Haruki Yamamoto, Jiro Harada, Taichi Yoshitomi, Jiro Nomata, Masahiro Kasahara, Tadashi Mizoguchi, Yuichi Fujita, Hitoshi Tamiaki. An unexpectedly branched biosynthetic pathway for bacteriochlorophyll b capable of absorbing near-infrared light. Scientific reports. 2013;3:1217

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PMID: 23386973

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