Biology Reference
In-Depth Information
protection of critical cysteines against irreversible oxidation (sulfinic and
sulfonic acids) during oxidative stress (
Masip, Veeravalli, & Georgiou, 2006
),
and as a post-translational regulatory modification (
Dalle-Donne, Rossi,
Colombo, Giustarini, & Milzani, 2009
;
Rouhier, Lemaire, & Jacquot, 2008
;
Zaffagnini, Bedhomme, Marchand, Morisse, Trost, & Lemaire, 2012
).
The ROS oxidants can be detoxified by various metabolites (ascorbate,
carotenoids, glutathione, vitamins, etc.) and several enzymes. The enzymes -
superoxide dismutase (SOD), catalase and peroxidase - sequentially con-
vert the superoxide anion to hydrogen peroxide (SOD) and subsequently
hydrogen peroxide to water (catalase and peroxidase) (
Imlay, 2008
;
Latifi
et al., 2009
;
Masip et al., 2006
). By contrast, the protein disulfides and
glutathione-protein mix disulfides are repaired by thioredoxins (
Berndt,
Lillig, & Holmgren, 2008
) and glutaredoxins (
Lillig, Berndt, & Holmgren,
2008
;
Zaffagnini, Bedhomme, Marchand et al., 2012
). If and when the oxi-
dants outnumber the anti-oxidants, the resulting oxidative stress can lead
to cell death in microorganisms and pathologies in mammals. In addition,
the ROS species, more particularly H
2
O
2
, can also operate in signalling,
which is an important physiological process (
Forman et al., 2010
). Indeed,
H
2
O
2
possesses the required properties to be a secondary messenger in
being enzymatically produced and degraded by the superoxide dismutase
and catalase enzymes, respectively. Furthermore, H
2
O
2
oxidizes protein thi-
ols in disulfides, which can be reduced back to thiols, are thereby relevant as
thiol redox switches for signalling.
This review outlines the variety of the processes used by cyanobacte-
ria to protect themselves against oxidative stress, emphasizing on glutathi-
one and the wealth of glutathione-dependent enzymes, which have been
well conserved during evolution (
Couturier, Jacquot, & Rouhier, 2009
;
Dalle-Donne et al., 2009
;
Masip et al., 2006
).
2. GLUTATHIONE AN INTEGRATIVE LINK BETWEEN
CELL METABOLISM AND THE DEFENCES AGAINST
OXIDATIVE AND METAL STRESSES
2.1. The Pleiotropic Roles of Glutathione
Various metabolites as alpha tocopherol (vitamin E), carotenoids (beta-
carotene, myxoxanthophyll, zeaxanthin), and glutathione (the tripeptide
γ-L-glutamyl-L-cysteinyl-L-glycine) operate in the defence against ROS
(
Latifi et al., 2009
;
Masip et al., 2006
). Glutathione (GSH) is one of the
most abundant cellular thiols (concentration ranging from 0.1 to about
