Biology Reference
In-Depth Information
singlet oxygen, mainly involving addition to
the double bonds and describing the general
chemical damage caused in biomolecules;
Deactivation of singlet oxygen: kinetics and
mechanisms , describing the operational
kinetics and mechanisms of singlet oxygen
suppression; Natural defences and suppres-
sors of singlet oxygen , unravelling properties
of singlet oxygen suppressors, establishing
structure/activity relationships for several
classes of molecules in nature, including
carotenoids, catechins, flavonoids, lycopene
and tannins.
Ames, 1998). The discovery of antioxidant
enzymes and molecules (McCord and
Fridovic, 1969; Beckman and Ames, 1998;
Halliwell, 2009), and their roles in signal-
ling and defence, brought into perspective
the beneficial aspects of free radicals. The
general view today is that living organisms
not only have learnt to survive the chemi-
cal hazards presented by ROS and NOS but
also have learnt to take advantage of the
diversity of reactivities offered by them
(McCord and Fridovic, 1969; Halliwell,
2009). There are several enzymatic reac-
tions that lead to the production of free
radicals including the electron transport
chain in mitochondria, which is a major
and continuous source of ROS (Kowaltowski
and Vercesi, 1999). In a sense it is difficult
to think of life without thinking of free
radicals.
Redox homeostasis is kept in a steady
state owing to a balance between the rate of
formation of ROS and NOS and the rate of
their suppression. However, the rate of free-
radical production may surpass the rate of
their suppression and a situation of redox
misbalance is obtained (Fig. 6.1), which is
implicated in a series of physiological and
pathological conditions in living organisms.
6.2
Redox Misbalance
Since the initial observation of free radicals
in biological materials more than 50 years
ago, the generation of several reactive oxy-
gen species (ROS) and nitrogen species
(NOS) have been proved to occur in differ-
ent conditions, concentrations and exerting
diverse roles (Commoner et al ., 1954;
Augusto et al ., 2002; Halliwell et al ., 2009).
Free radicals have been related to cell death,
cancer, ageing and diverse degenerative
processes (Harman, 1981; Beckman and
Exposure to UV, VIS, IR
Xenobiotics
Anti-inflammatory
Inflammation
Protein oxidation
and lipid
peroxidation
Antioxidants
Oxidants
DNA damage
Necrosis
Apoptosis
Tumour
destruction
Cancer
Fig. 6.1. Oxidation misbalance caused by sun exposure and/or a xenobiotic and its effect in eukaryotic cells.
 
Search WWH ::




Custom Search