Oxidation response
Such a global response induces an adaptive metabolism including ROS elimination, the bypass of injured pathways, reparation of oxidative damages and maintenance of reducing power.
The oxidized form of this factor specifically binds to the promoters of constituent genes of OxyR regulon, including katG (hydroperoxidase-catalase HPІ), gorA (glutathione reductase), grxA (glutaredoxin 1), trxC(thioredoxin 2), ahpCF (alkyl hydroperoxide reductase), dps (nonspecific DNA binding protein) and oxyS (a small regulatory RNA).
The structural genes under this regulon include sodA (Mn-superoxide dismutase(SOD)), zwf (glucose-6-phosphate dehydrogenase(G6PDH)), acnA (aconitase A), nfsA (nitrate reductase A), fumC (fumarase C) and nfo (endonuclease IV) among others.
In E.coli, negative autoregulation of SoxS protein serves as a dampening mechanism for the soxRS redox stress response.
[2] At least three known genes including xthA and katE are regulated by a sigma factor, KatF(RpoS), whose synthesis is turned on during the stationary phase.
The enzymatic components may directly scavenge active oxygen species or may act by producing the nonenzymatic antioxidants.
This occurs in the following steps: (i) thioredoxin reductase transfers electrons from NADPH to thioredoxin via a flavin carrier (ii) glutaredoxin is also able to reduce disulfide bonds, but using GSH as an electron donor (iii) protein disulfide isomerase facilitates disulfide exchange reactions with large inactive protein substrates, besides having chaperone activity Oxidation of surface exposed methionine residues surrounding the entrance to the active site could function as a “last-chance” antioxidant defense system for proteins.
Most mammalian cells exist in an environment where the oxygen concentration is constant, thus responses are not directly stimulated by oxidants.
The similarities include increased oxidation of cellular constituents and its target specificity, the role of antioxidants and oxygen tension in determining life span, and an apparent trade-off between activities related to reproduction and survival.
