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Updated: May 10, 2026

Isolation and Characterization of Intact Phycobilisome in Cyanobacteria
Published on: November 10, 2021
Completion of biosynthetic pathways for bacteriochlorophyll g in Heliobacterium modesticaldum: The C8-ethylidene
Yusuke Tsukatani1, Haruki Yamamoto, Tadashi Mizoguchi
1Graduate School of Life Sciences, Ritsumeikan University, Shiga 525-8577, Japan. yusuke-t@fc.ritsumei.ac.jp
Abstract:
Heliobacteria have the simplest photosynthetic apparatus, i.e., a type-I reaction center lacking a peripheral light-harvesting complex. Bacteriochlorophyll (BChl) g molecules are bound to the reaction center complex and work both as special-pair and antenna pigments. The C8-ethylidene group formation for BChl g is the last missing link in biosynthetic pathways for bacterial special-pair pigments, which include BChls a and b as well. Here, we report that chlorophyllide a oxidoreductase (COR) of Heliobacterium modesticaldum catalyzes the C8-ethylidene formation from 8-vinyl-chlorophyllide a, producing bacteriochlorophyllide g, the direct precursor for BChl g without the farnesyl tail. The finding led to plausible biosynthetic pathways for 8(1)-hydroxy-chlorophyll a, a primary electron acceptor from the special pair in heliobacterial reaction centers. Proposed catalytic mechanisms on hydrogenation reaction of the ethylidene synthase-type CORs are also discussed.
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