1. SARAH ASHFAQ
BSADP-BT51F21
BS 5th Sem. ADP Replica
Presented To : Dr. Zahoor Ahmad Sajid
Topic: Antioxidant Enzymes
Institute Of Botany , University Of The Punjab
2. ENZYMES:
“An enzyme is a protein which
speed up biochemical reactions”
They build some substances and
break others down.
All living things have enzymes.
3. ANTIOXIDANT ENZYMES:
“Antioxidant enzymes
are capable of stabilizing, or
deactivating free radicals before
they attack cellular components.
They act by reducing the energy
of the free radicals or by giving
up some of their electrons for
its use, thereby causing it to
become stable.”
4. How do antioxidants work?
Antioxidants neutralize free radicals by giving up some of their
own electrons. In making this sacrifice, they act as a natural
"off" switch for the free radicals.
This helps break a chain reaction that can affect other
molecules in the cell and other cells in the body.
5. Free Radicals:
• “A molecule with one or more unpaired electron in its outer shell is called a free radical .
• A balance between free radicals and antioxidants is necessary ion.
• Free radicals and oxidants play a dual role as both toxic and beneficial compounds, since
they can be either harmful or helpful to the body.
• They are produced either from normal cell metabolisms or from external sources
(pollution, cigarette smoke, radiation, medication).
• When an overload of free radicals cannot gradually be destroyed, their accumulation in
the body generates a phenomenon called oxidative stress.
7. Reactive Oxygen Species:
Reactive oxygen species (ROS) are natural by products of cellular oxidative
metabolism and play important roles in the modulation of cell survival, cell death,
differentiation, cell signaling, and inflammation-related factor production.
Reactive oxygen species (ROS) are highly reactive chemicals formed from O2.
Examples of ROS include peroxides, superoxide, hydroxyl radical, singlet
oxygen, and alpha-oxygen.
9. 1.GLUTATHIONE PEROXIDASE:
• The biochemical function of glutathione peroxidase is to reduce lipid hydroperoxides to their
corresponding alcohols and to reduce free hydrogen peroxide to water.[
• Glutathione peroxidase 1 (GPx1) is the most abundant version, found in the cytoplasm of nearly all
mammalian tissues, whose preferred substrate is hydrogen peroxide.
• Reactions:
• The main reaction that glutathione peroxidase catalyzes is:
• 2GSH + H2O2 → GS–SG + 2H2O
• GSH represents reduced monomeric glutathione, and GS–SG represents glutathione disulfide. The
mechanism involves oxidation of the selenol of a selenocysteine residue by hydrogen peroxide.
• Glutathione reductase then reduces the oxidized glutathione to complete the cycle:
• GS–SG + NADPH + H+ → 2 GSH + NADP+.
11. 2.GLUTATHIONE
REDUCTASE:
Glutathione reductase
is responsible for maintaining the
supply of reduced glutathione; one
of the most abundant reducing
thiols in the majority of cells. In
its reduced form, glutathione plays
key roles in the cellular control of
reactive oxygen species
12. 3.CATALASE:
Catalases are enzymes that catalyse the conversion of hydrogen peroxide
to water and oxygen, using either an iron or manganese cofactor.
This is found in peroxisomes in most eukaryotic cells.
Its only substrate is hydrogen peroxide.
It follows a ping-pong mechanism.
Sources: Cruciferous vegetables, including broccoli, cabbage, kale and
collard and turnip greens, are rich in catalase.
Eating plenty of these green leafy vegetables also stimulates your body's
production of catalase
13. Ping Pong Mechanism:
Ping Pong is also called
the double placement
reaction and it means that one or
more products are released before
all substrates bind the enzyme.
One key character of this reaction
is the existence of a substituted
enzyme intermediate.
14. 4.SUPEROXIDE DISMUTASE:
• Superoxide dismutase (SODs) are a class of
enzymes that catalyse the breakdown of the
superoxide anion into oxygen and hydrogen
peroxide.
• These enzymes are present in almost all aerobic
cells and in extracellular fluids.
• SODs contain metal ion cofactors that,
depending on the isozyme .It can be copper,
zinc, manganese or iron. For example, in
humans copper/zinc SOD is present in the
cytosol, while manganese SOD is present in the
mitochondrion. The mitochondrial SOD is most
biologically important of these three.
• In plants, SOD isozymes are present in the
cytosol and mitochondria.
• There is also an iron SOD found in chloroplasts.
16. 5.Ascorbate Peroxidase
(APX):
Ascorbate peroxidase (APX) is
also a H2O2-scavenging
enzyme and is indispensable for
the protection of chloroplasts and
other cell constituents from
damage by H2O2 and hydroxyl
radicals (•OH).
17. 6. Monodehydroascorbate
reductase (MDAR) :
In enzymology,
a monodehydroascorbate
reductase (MDAR) is
an enzyme that catalyzes the
chemical reaction:
NADH + H⁺ + 2 monodehydroascorbate--NAD⁺ + 2
ascorbate
18. Dehydroascorbate
reductase (DHAR):
Dehydroascorbate reductase (DHAR)
is a key enzyme involved in the
recycling of ascorbate, which
catalyses the glutathione (GSH)-
dependent reduction of oxidized
ascorbate (dehydroascorbate, DHA).
As a result, DHAR regenerates a pool
of reduced ascorbate and detoxifies
reactive oxygen species (ROS).
