Biology Reference
In-Depth Information
Oxygen Suppressors
Adjaci F. Uchoa,* Divinomar Severino and Mauricio S. Baptista
Department of Biochemistry, Chemistry Institute,
University of São Paulo, Brazil
6.1
Introduction
Nature looks for strategies to protect
itself from these inconveniences. For protec-
tion against sunlight, humans have melanin
to avoid light from reaching proliferative
cells in the epidermis. Plants, on the other
hand, make use of their secondary metabo-
lites in an appropriate and necessary way to
suppress
1
O
2
. Countless antioxidants, such
as flavonoids, anthocyanins, ascorbic acid,
carotenoids, lycopene, tannins and vitamin A,
have been described to suppress
1
O
2
.
Many of these substances are synthesized
from the phytoene or shikimic acid pathway,
which is not present in animals. Therefore,
when humans ingest these substances they
benefit from their protection activities. We
have organized this chapter into five topics
that are:
Redox misbalance
, discussing the
interaction of light of different wavelengths
with different organisms inducing the for-
mation of reactive oxygen species with an
emphasis on singlet oxygen;
Singlet oxygen:
general properties, detection methods and
biological roles
, discussing important
aspects of the chemical/biochemical proper-
ties, generation and detection of singlet oxy-
gen (damage to proteins of the photosynthetic
apparatus and membranes in general will be
discussed in detail);
Chemical reactivity
,
describing the main reaction routes of
Molecular oxygen is unusual amongst com-
mon molecules in having a triplet ground
state. The two electronically excited states
immediately above the ground state are both
singlet states: one, designated
1
S
g
+
state, has a
very short lifetime (less than a picosecond),
and rapidly decays to the lower singlet state,
designated
1
D
g
state, which has a lifetime of a
few microseconds in water and is the main
species reacting in the biological environ-
ment. Singlet oxygen (
1
O
2
) is an extremely
reactive electrophilic species. It attacks with
great efficiency highly alkylated double
bonds, inducing damage in membranes,
proteins and DNA. Its overproduction can
lead to a degenerative disease called porphy-
ria or to tumours and other human diseases
in the process called photodynamic therapy.
Damage in the membranes can be initi-
ated by the formation of lipid hydroperox-
ides, which can progress to cause membrane
peroxidation and end up causing premature
photo-ageing in the skin. The side groups of
several amino acids are susceptible to oxidi-
zation by singlet oxygen, causing changes in
the structure of the proteins and loss of
activity, affecting, for example, the effi-
ciency of photosynthesis.
* E-mail: adjaci@usp.br
Search WWH ::
Custom Search