The secondary electron acceptor of photosystem I in Gloeobacter violaceus PCC 7421 is menaquinone‐4 that is synthesized by a unique but unknown pathway

Abstract

The secondary electron acceptor of photosystem (PS) I in the cyanobacterium Gloeobacter violaceus PCC 7421 was identified as menaquinone-4 (MQ-4) by comparing high performance liquid chromatograms and absorption spectra with an authentic compound. The MQ-4 content was estimated to be two molecules per one molecule of chlorophyll (Chl) a 0 , a constituent of P700. Comparative genomic analyses showed that six of eight men genes, encoding phylloquinone/MQ biosynthetic enzymes, are missing from the G. violaceus genome. Since G. violaceus clearly synthesizes MQ-4, the combined results indicate that this cyanobacterium must have a novel pathway for the synthesis of 1,4-dihydroxy-2-naphthoic acid.

Variations in Photosystem I Properties in the Primordial Cyanobacterium Gloeobacter violaceus PCC 7421

“…The photochemical activity of our preparations was high, consistent with our previous study (14). The difference maximum for the P700 spectrum of the G. violaceus PS I complexes (Fig.…”

“…In G. violaceus , P700 most likely consists of one Chl a and one Chl a ′ molecule, because Chl a ′ is stoichiometrically present in this species (14). The redox potential of G. violaceus P700 is lower than that of Synechocystis sp.…”

“…In their stead, a new subunit, PsaZ, is found in this bacterium (13). The secondary electron acceptor, a quinone molecule, is menaquinone (MQ‐4) (14), instead of phylloquinone, which is found in other oxygenic photosynthetic organisms. MQ‐4 is found in photosynthetic bacteria, and G. violaceus may have a novel biosynthetic pathway for this molecule, because several genes for its synthetic enzymes in other bacteria are missing in G. violaceus .…”

Characterization of Highly Purified Photosystem I Complexes from the Chlorophyll d-dominated Cyanobacterium Acaryochloris marina MBIC 11017

“…Even though the presence of Chl a was not evident in the absorption spectra, it was unambiguously demonstrated by the fluorescence excitation spectra. Ϫ1 h Ϫ1 , respectively (52). FTIR Spectra-The special pair of PS I in A. marina was assigned to a Chl d dimer (20,21) and further to a Chl d/Chl dЈ heterodimer in consideration of the pigment content (32) and the x-ray crystallographic structure of T. elongatus PS I (4).…”

Menaquinone as Well as Ubiquinone as a Crucial Component in the Escherichia coli Respiratory Chain

“…Green filamentous bacteria dominantly utilize MK-10 both for photosynthetic and respiratory electron transport reactions (Hale et al, 1983). MK-4 is present in the PSI of the cyanobacterium Gloeobacter violaceus or Synechococcus PCC 7002 diatoms and primitive red alga C. caldarum (Ikeda et al, 2008;Mimuro et al, 2005;Sakuragi et al, 2005). Green sulfur bacteria contain MK-7 in their PSI-type RCs (Hauska et al, 2001), similar to that of PSI of green filamentous bacteria.…”