2. Introduction
• Oxidoreductase is an enzyme that catalyzes the
transfer of electrons from one molecule to another.
• The reductant is called as electron donor.
• The oxidant, also called the electron acceptor.
• This group of enzymes usually utilizes
NADP or NAD+ as cofactors.
3. Example
• For example, an enzyme that catalyzed this reaction would
be an oxidoreductase:
• A– + B → A + B–
• In this example, A is the reductant (electron donor) and
B is the oxidant (electron acceptor)
• Pi + glyceraldehyde-3-phosphate + NAD+ → NADH + H+ +
1,3-bisphosphoglycerate
• In this reaction, NAD+ is the oxidant (electron acceptor),
and glyceraldehyde-3-phosphate is the reductant (electron
donor).
4. Glucose oxidase
• The glucose oxidase enzyme (GOx) is an oxido-reductase that
catalyses the oxidation of glucose to hydrogen
peroxide and D- glucono lactone.
• In cells, it aids in breaking the sugar down into its metabolites.
• In order to work as a catalyst, GOx requires a cofactor, flavin
adenine dinucleotide (FAD). FAD is a common component in
biological oxidation-reduction (redox reactions).
5. Source of glucose oxidase
• Most common source of glucose oxidase is
Aspergillus niger
6. Applications of glucose oxidase
• Glucose oxidase is widely used for the determination of free
glucose in body fluids (diagnostics)
• Glucose oxidase is found in honey and acts as a natural
preservative. GOx at the surface of the honey reduces
atmospheric O2 to hydrogen peroxide (H2O2) which acts as
an antimicrobial barrier
• GOx similarly acts as a bactericide in many cells (fungi,
immune cells).
7. Cont…..
• Glucose oxidase removes D-glucose from egg white
to prevent browning.
• GOx also used to monitor glucose levels in
fermentation, bioreactors, and to control glucose in
food products.
8. Glucose assay
• In the glucose oxidase assay, the glucose is first oxidized by
glucose oxidase to produce gluconate and hydrogen peroxide.
• The hydrogen peroxide is then oxidatively coupled with
a chromogen to produce a colored compound
• which is then measured spectroscopically at 505nm.
9. Catalase
• Catalase catalyzes the decomposition of hydrogen
peroxide to water and oxygen.
• It is a very important enzyme in protecting the cell
from hydrogen peroxide
• Catalase has one of the highest turnover numbers of all
enzymes; one catalase molecule can convert approximately 5
million molecules of hydrogen peroxide to water and oxygen
each second.
10. Cont…
• Catalase is a tetramer of four polypeptide chains, each over
500 amino acids long
• It contains four porphyrin heme (iron) groups that allow the
enzyme to react with the hydrogen peroxide
• he pH optimum for other catalases varies between 4 and 11
depending on the species. The optimum temperature also
varies by species.
11. History of Catalase
• Catalase was not noticed until 1818 when Louis Jacques
Thénard, who discovered H2O2 (hydrogen peroxide),
suggested its breakdown is caused by an unknown substance.
• In 1900, Oscar Loew was the first to give it the name catalase
• In 1937 catalase from beef liver was crystallised by James B.
Sumner
12. Reaction of catalase
• The reaction of catalase in the decomposition of hydrogen
peroxide in living tissue:
• 2 H2O2 → 2 H2O + O2.
• The presence of catalase in a microbial or tissue sample can be
tested by adding a volume of hydrogen peroxide and observing
the reaction.
• The formation of bubbles, oxygen, indicates a positive result.
13. Application
• Catalase is used in the food industry for removing hydrogen
peroxide from milk prior to cheese production.
• Removing hydrogen peroxide from fabrics to make sure the
material is peroxide-free to prevent browning
14. Polyphenol oxidase
• Polyphenol oxidase (PPO) also known as monophenol
monooxygenase tetramer that contains four atoms of copper
per molecule
• PPO causes the rapid polymerization of quinones to produce
black, brown or red pigments (polyphenols) that cause fruit
browning.
• The amino acid tyrosine contains a single phenolic ring that
may be oxidised by the action of PPOs to form o-quinone.
Hence, PPOs may also be referred to as tyrosinase.
15. Source of Polyphenol oxidase
• Enzyme mainly present in plastid (chlroplast)
• Common plant food examples producing the enzyme
are mushrooms, apples and lettuce
16. Application of Polyphenol oxidase
• Used to remove toxic phenol (pollutant)
• To remove toxic pesticides from food product
17. L-ascorbate oxidase
• L-ascorbate oxidase is an enzyme that catalyzes the chemical
reaction
• 2 L-ascorbate + O2 2 dehydroascorbate + 2 H2O
• Thus, the two substrates of this enzyme are L-
ascorbate and O2, whereas its
two products are dehydroascorbate and H2O.
• This enzyme participates in ascorbate metabolism. It employs
one cofactor, copper.
18. Applications of L-ascorbate oxidase
• Ascorbate Oxidase is useful for enzymatic determination of
ascorbic acid and for
• Enzyme also used in elimination of ascorbic acid in clinical
analysis.
