Microbiology news and views
J. Mol. Micro. Biotechnol. 3: 273-283
The Diheme Cytochrome b Subunit (NarI) of
Escherichia coli Nitrate Reductase A (NarGHI): Structure, Function, and
Interaction with Quinols
Richard A. Rothery, Francis Blasco, Axel Magalon, and Joel H. Weiner
Significant recent advances have been made in studies of the major dissimilatory nitrate reductase (NarGHI)
of Escherichia coli. This enzyme is a complex iron-sulfur ([Fe-S]) molybdoenzyme that oxidizes menaquinol
or ubiquinol at a periplasmically oriented Q-site
(QP site), and reduces nitrate at a cytoplasmically-oriented
molybdo-(bismolybdopterin guanine dinucleotide) (Mo-bisMGD) cofactor. The
QP site, as well as two hemes, termed
bL and bH, are localized in a hydrophobic diheme cytochrome
b (NarI) that: (i) provides a conduit for
electron-transfer from the periplasmically-oriented
QP-site; (ii) provides a membrane anchoring functionality for
the membrane-extrinsic subunits (NarGH) that coordinate the Mo-bisMGD (NarG) and four [Fe-S] clusters
(NarH); and (iii) helps ensure the separation of sites of
H+-yielding and H+-consuming reactions such that
enzyme turnover leads to the generation of a proton-electrochemical potential across the cytoplasmic membrane.
This minireview focuses on recent advances and future prospects for the diheme cytochrome
b subunit (NarI) of NarGHI.
Full article [pdf]
New and forthcoming molecular biology books
Recommended Reading