ANTIOXIDANT / OXIDANT BALANCE:
Antioxidant /
Oxidant Balance:
Health = Oxidant / Antioxidant Balance - Meet Dr. ROS Jeckyll
Dr. ROS Jeckyll
In biological systems, REDOX reactions
using the OXIDANT ability of Reactive Oxygen
Species (ROS) are essential to body's functions maintaining life
When we say Oxygen "OXIDIZES" Food, What Does that Mean?
Oxygen Molecule (3
O2 ) "Activated" to Produce ROS by 2 Different Mechanisms
ROS production
in the body can be Enzymatically or Non-enzymatically mediated
ROS
are produced continuously in cells either as by-products
of metabolism or deliberately as in immune system phagocytosis.
They are also by-products of circulation, respiration, digestionand assimilation.
REDOX (REDuction/OXidation)
REACTION - This chemical term refers to a two-way
reaction in which:
One atom or molecule (REDUCTANT) - GIVES away an
electron (REDuces)Another atom or molecule (OXIDANT) - TAKES an
electron (OXidizes).
When we say Oxygen "OXIDIZES" Food, What Does that Mean?
Oxygen is responsible for providing energy for the
cell in a process called "cellular respiration".
This takes
place in the cell mitochondria ("energy
factories').
Oxygen (the "oxidant"
in this REDOX reaction) "oxidizes" (
removes electrons from)
glucose (Electrons are transferred
from the sun's radiant energy to
glucose in food, via chlorophyll) and then uses the 4
electrons it acquires
to produce energy.
Electrons are
removed from glucose in a series of enzyme-assisted steps, which pass them along
an "Electron Transport Chain"until they are finally accepted by
oxygen , producing
water. Glucose is the "reductant"
in this redox reaction, since
glucose "reduces"(gives away electrons to)
oxygen .
The
energy gained
in this process is stored (via a process called "oxidative phosphorylation")
as ATP
molecules
Cellular Respiration
Oxygen Molecule ( 3 O2 )
May be "Activated" to Produce ROS
in the body by 2 Different Mechanisms(1) By Excitation:
If atmospheric Oxygen ( 3
O2 )
absorbs sufficient energy to reverse
the spin of one of its unpaired electrons,
it will form the
ROS
singlet oxygen ,
in which its two unpaired electrons have
opposite spins.
Singlet oxygen
triplet oxygen ,
and can thus participate in reactions involving the simultaneous transfer
of two electrons (divalent reduction). Since paired electrons are common in organic
molecules,
singlet oxygen is much more
reactive towards organic molecules than
3
O2
.
Singlet oxygen
(Photodynamic Therapy -provides benefit of light therapy on photosensitive
molecules purposefully introduced to target areas off body)
(2) By reduction:
In the body, ROS
are more typically produced by the progressive reductionof
Oxygen to form
Superoxide , Hydrogen
Peroxide ,
Hydroxyl Radical and
finally water.
The energy-producing cellular respiration chain in the mitochondria (the
energy "factory" of cell)uses more than 90% of the body's
oxygen ,2 ) and energy. The summary process of how cells
produce energy from glucose in the presence of sufficient oxygen is:
C6 H12 6
(glucose) + 6 3 O2 →
6 CO2
2 O+
Energy
These partial equations show the intermediate
ROS produced during this 4-step process:
1
3
O2 +e
- →O2
Superoxide Radical
(mildly reactive)
Adding 1e-
to molecular
oxygen
2
O2 •
-- 2 O→HO2 •
OH--
Hydroperoxyl Radical (highly reactive)
Adding H to
Superoxide
3
HO 2 •
+e- +
H
H2 O2
Hydrogen Peroxide (poorly reactive)
Adding 2 e -
oxygen
4
H2 O2 +e- →
OH • +OH--
Hydroxyl Radical (extremely reactive)
Adding 1e- to
Hydrogen peroxide
Enzymatically
or Non-enzymatically mediatedEnzymatic oxidation:
Oxidases:
enzymes that catalyze the reaction when oxygen is the acceptor of hydrogen to form water or
H2O2 Hydroperoxidases
and peroxidases: use H2 O or ROOH as oxidizing agent;Dehydrogenases:
catalyse dehydrogenation of a substrate using NAD+ or NADP+ Oxygenases:
incorporate oxygen into substrate
A variety of enzyme systems are capable of generating
significant amounts of
free radicals ,
including:
Xanthine
oxidase. Activated in ischemia / reperfusion
(reduction / restoration of blood supply to an organ or tissue caused by constriction
or obstruction of the blood vessels, E.g. after a heart attack).
Lipoxygenase enzymes catalyze reactions
between 3
2 PUFAs (polyunsaturated fatty acids), such
as arachidonic acid (AA), containing methylene
interrupted double bonds.HETEs ).
Cyclooxygenase (COX) enzymes catalyze the
addition of 3
O2 to various
PUFAs, converting them into biologically active molecules called endoperoxides(PGG,
PGH ) - intermediates in the transformation of fatty acids to prostaglandins.
Myeloperoxidase
- produced in neutrophils, monocytes and newly activated
macrophages, catalyses
hydrogen peroxide's
oxidation of chloride ions into the powerful oxidant
hypochlorous acid (HOCl)
Prostaglandin
synthase
Aldehyde
oxidase
Amino
acid oxidase.
Non-enzymatic
(Autoxidation):Autoxidation is a by-product of the aerobic internal
milieu - molecules that undergo autoxidation include:
Catecholamines
Haemoglobin
Myoglobin
(in heavily exercised muscles)
Rreduced
cytochrome C
Thiol.
Autoxidation of any
of the above molecules in a reaction results in the reduction of
3 O2
and the formation of
ROS - Superoxide
is the primary radical formed.
A ferrous ion
(Fe II) also, can have its
electron stolen from it by oxygen to produce
superoxide and Fe III - by the process of autoxidation (Fridovich,
1983 and 1995)
