1. ENZYME: ITS MODE OF ACTION
By
KAUSHAL KUMAR SAHU
Assistant Professor (Ad Hoc)
Department of Biotechnology
Govt. Digvijay Autonomous P. G. College
Raj-Nandgaon ( C. G. )
3. Property of enzyme
Structure of enzyme
Mechanism of enzyme action
Lock and key model
Induced fit model
factors affecting enzyme
activity
Control of enzyme action
Conclusion
Reference
4. Introduction :-
•Enzymes are biocatalysts. The catalyst of life. A catalyst is defined as a
substance that increases the velocity or rate of a chemical reaction without
itself undergoing any change in the overall process.
•In the 1850s LOUIS PASTEUR concluded that fermentation of sugar into
alcohol by yeast is catalyzed by ‘’ferments’’. He postulated that these
ferments were in separable from the structure of living yeast cells. This view
called vitalism prevailed for decades.
•Then in 1897 EDWARD BUCHNER discovered that yeast extract ferment
sugar to alcohol proving that fermentation was promoted by molecules that
continued to function when remove from cells. FREDERICK W. KUHNE
called these molecules enzymes.
Father of enzymology :- The isolation & crystallization of urease by
James Sumner in 1926 provided a break through in early enzymes.
5. Definition :-
ENZYMES
Enzyme may be defined as biocatalyst
synthesized by living cells. They are protein
in nature colloidal & thermo labile in
character & specific in their reaction.
SUBSTRATE
In enzymatic reactions, the molecules at the
beginning of the process are called
substrates.
6. Historical Aspects
.
The various aspects has been evaluated as in year :-
•In year 1857 LOUIS PASTEUR classified the role of yeast in fermentation &
evolved germ theory of diseases & founded the science of BACTERIOLOGY.
•In 1833 – PAYEN AND PESOZ prepared enzyme diastase (amalyase).
•HORACEDE SAUSSURE – Prepared germinating wheat acted like diastase.
•THEODOR SCHWANN – Extra acting pepsine.
•IN 1836 – BERZELIUS coined the term catalysis.
•In1857– PASTEUR demonstrated alcoholic fermentation by living yeast cell.
•In 1878 – W. KUHNE used enzyme as ferments.
•In 1883 – EDUARD BUCHNER isolated enzyme from cell free extract of
yeast and denoted as zymase.
•In 1926 – JAMES SUMNER.
7. NOMENCLATURE OF ENZYMES
•Enzymes are generally named by adding ‘ase’ to the root indicating
the substrate on which the enzymes acts.
Eg. Fumarase catalyses the conversion of fumaric acid to malic acid.
•In the early days the enzymes were given names by their discoverers
in an arbitrary manner for example the names pepsin, trypsin &
chymotrypsin convey no information about the function of the enzyme
of the nature of the substrate on which they act.
•Sometimes the suffix – ase was added to the substrate for naming
the enzymes lipase acts on lipid , nuclease on nucleic acid , lactase
on lactose. These are known as trivial names of enzymes which
however fail to give complete information of enzymes reaction.
8. Nomenclature of enzymes on the basis of:
•Substrate acted upon by the enzymes :-
The substance upon which an enzyme acts is called the substrate.
For ex. – Enzymes acting upon carbohydrates were named as
carbohydrase, upon protein as proteinase, upon lipid as lipase and so on
etc.
•Types of reaction catalyzed :-
The enzyme are highly specific as to the reaction they catalyze.
For ex. – hydrolase ( catalyzing hydrolysis ), isomerase (isomerization),
dehydrogenase (dehydrogenation), transketolase (transketolation) etc.
•Substrate acted upon a type of reaction catalyzed :-
The names of some enzymes give clue of both the substrate
utilized & the type of reaction catalyzed.
For ex. – The enzyme succinic dehydrogenase catalyzes the
dehydrogenation of the substrate succinic acid. Similarly L – glutamic
dehydrogenase indicates an enzymes catalyzing a dehydrogenation
reaction involving L – glutamic acid.
9. Types of enzymes :- Enzymes are sometimes considered
under two broad categories :-
Intracellular Enzymes :- They are functional with in cells
where they are synthesized.
Extracellular Enzymes :- These enzymes are active out side
the cell. All the digestive enzymes belong to this group.
Nomenclature of enzymes on the basis of:
•Substrate acted upon by the enzymes :- The substance upon
which an enzyme acts is called the substrate.
For ex. – Enzymes acting upon carbohydrates were named as
carbohydrase, upon protein as proteinase, upon lipid as lipase
and so on etc.
•Types of reaction catalyzed :- The enzyme are highly specific
as to the reaction they catalyze.
For ex. – hydrolase ( catalyzing hydrolysis ), isomerase
(isomerization), dehydrogenase (dehydrogenation),
transketolase (transketolation) etc.
10. Substrate acted upon a type of reaction catalyzed :-
The names of some enzymes give clue of both the
substrate utilized & the type of reaction catalyzed.
For ex. – The enzyme succinic dehydrogenase catalyzes the
dehydrogenation of the substrate succinic acid. Similarly L
– glutamic dehydrogenase indicates an enzymes catalyzing
a dehydrogenation reaction involving L – glutamic acid.
Types of enzymes :- Enzymes are sometimes considered
under two broad categories :-
Intracellular Enzymes :- They are functional with in
cells where they are synthesized.
Extracellular Enzymes :- These enzymes are active out
side the cell. All the digestive enzymes belong to this
group.
11. Classification of enzyme that is precise, description and informative
is based on IUB system:-
The international union of biochemistry appointed an enzyme
commission in 1961 .This committee made through study of the
existing enzymes and devised some basic principles for the
classification and nomenclature of enzyme.
Enzyme are divided in to 6 major class (in that order). Each class
on its own represents the general types of reaction brought about
by the enzyme of that class with example :-
1. Oxidoreductases :-
Enzyme involved in Oxidation reduction reactions.Ex :- Alcohol
dehydrogenase , cytochrome oxidase , L & D amino acid
Oxidases .
2. Transferases :-
Enzyme that catalyses the
transfer of functional group.
Ex :- Hexokinase, transaminases, phosphrylase.
3. Hydrolases :- Enzyme that bring about
hydrolysis of various compounds.
Ex :- Lipase, Choline, esterase acid & alkaline
Phosphatases.
12. 4. Lyases :- Enzyme specialized in the addition or removal of
water, amonia,CO2.
Ex:- Aldose, fumarase, histidase.
5.Isomerase :- Enzyme involved in all the isomerization
reaction.
Ex :- Triose phosphate isomerase, phosphohexose isomerase.
6. Ligases :- Enzyme catalyzing the synthetic reaction (Greek
:- uigate –to bind) where two molecules are joined together
ATP is used.
Ex :- Glutamine synthetase, acetylCOA carboxylase.
13. Property of Enzyme :-
1) Enzyme are proteinous in nature and of colloidal nature .
2) Enzyme are catalytic in nature as a particular enzyme
catalyzed a particular reaction ,( Measured by turn over
number).
Ex :- Carbonic anhydrase (600,000).
3) Enzyme are specific their action.
Ex :- Absolute group & optical specific.
4) Enzyme are thermo labile in nature .
14. Structure of Enzyme :-
Enzyme are protein and consist of single polypeptide chain. That
are made of amino acid unit linked by peptide bond. The
sequence number of 20 amino acid make up different enzyme.
Enzyme have three dimensional structure.
Ex:-Ribonuclease, Carboxypeptidase, chymotrypsin.
15.
16. Active site :-
The active site (active centre) of an enzyme represents as the
small region at which the substrate (S) bind and participates in the
catalysis.
As the substrate molecules are comparatively much smaller than
the enzyme molecules, there should be some specific region or site
on the enzyme for binding with the substrate. Such site of
attachment are variously called as
“Acitve site” OR Catalytic sites or “Substrate sites.”
17. MECHANISM OF ENZYME ACTION
The mode of action belong to catalysis that is the prime
function of enzymes catalysis taking place in biological system is
similar to non- biological catalysis .For any chemical reaction two
occur, the reaction have two be in an activated state. Through
this the enzyme substrate complex from.
In enzyme catalysis the substrate (s) combined with enzyme
(E). At active site to formed enzyme - substrate complex (ES).
That result in the formation of product.
E + S ES E + P
Enzyme substrate Enzyme-Substrate Complex Enzyme & product
A few theory have been put forwarded to explain made of action of
enzyme are as follows :-
18. 1.Lock and key model / Fischers template theory -
This theory was proposed by Emil Fischer (German
Biochemist ).It is the first model proposed to explain &
enzymes catalyzed reaction .According to this model the
structure /Conformation of enzyme is rigid. The substrate fit to
binding site just as key fit into proper lock. Thus the active site
of enzyme is rigid and preshaped template where only a specific
substrate can bind.
It may not give any scope of flexibility of enzyme .Hence the
model fails to explain many facts of enzymatic reaction and the
effect of allosteric modulators.
19. Evidences proving the existence of ES complex
The ES complex have been directly observed by electron
microscopy & X-ray crystallography.
The physical property of enzymes change frequantally upon
formation of a ES complex.
The enzyme substrate complex can be isolated in pure form.
A most general evidences for the existence of ES complex is
the fact that at a constant concentration of enzyme the
reaction rate increase with increase in the substrate
concentration until a maximum velocity is reached.
20. 2. Induced fit theroy /Koshland’s model -
In 1958 Koshland proposed a most acceptable and realistic model
for enzyme-Substrate complex formation. According to this the
active site is not rigid and preshaped. The features of substrate
binding site are present at nascent active site. The interaction of
substrate with enzyme induces a fit or a conformation changes and
enzymes resulting in the formation of strong substrate binding site
amino acid. Due to induced fit the appropriate of enzymes are
repositioned to from active site and bring about catalysis.
This model has sufficient experimental evidence form X-ray
diffraction and also explains the action of allosteric modulators and
competitive inhibition on enzymes.
21. Evidences in support of induced fit model
An illustration of the competitive inhibitor analogue
may also be given on contact with the true substrate
all group brought in to correct spatial orientation. But
attachment of a competitive inhibitor. Which is either
too “slim” or too “bulky” induced incorrect alignment.
22. Activation Energy
Energy required by reactant to undergo the reaction is
known as activation energy Ea. Reactant when heated attain Ea.
Enzymes increases speed of a chemical reaction.They lower Ea
of a reaction thus enabling it to occur at ordinary physiological
temperatures. When reaction proceeds from one direction to
another they have to overcome an energy barrier called the
activation energy. When enzymes combines with substrate to
from ES complex. Energy level of substrate is raised, & its
reacts faster.
23. Factor affecting Enzyme activity:-
1. Effect of temperature :- Enzyme action is greatly affected by
temperature .If the temperature is increase by 100C the rate
of most chemical reactions is doubled. However at 400C -600C
there is loss of enzyme activity because denaturation of protein
occurs at this temperature.
24. 2. PH :- At optimum pH the activity of
enzymes is maximum for most enzyme the effective
pH range is 4-9. Beyond these limits denaturation of
enzyme takes place. The optimum pH for pepsin is
2.0 & for trypsin 8
25. •Concentration :- Enzyme concentration affects the rate
of a reaction. If the the substrate concentration is
increased the rate of enzyme reaction also rises. Beyond a
certain pain however, the enzyme becomes saturated with
substrate molecules. Further increase in reaction velocity
occur only if the enzyme concentration is increased.
26. •Substrate Concentration :- Effect of substrate concentration
on enzyme activity when the maximum velocity has been
reached, all of the available enzyme has been converted to
Enzyme-substrate complex. The substrate complex (The point is
designated Vmax on graph) Km. shown refer to the Michaelis
constant and it is defined as the substrate concentration at one
half the maximum velocity.
27. Control of Enzyme action :-
The action of an enzyme can be controlled by its product
(Feed –back). Accumulation of the product slows down the rate
of chemical reaction .There is however, a more complicated
system of control in linked system. Many reaction is the cell
take place in a series of steps, each steps being controlled by a
separate enzyme for example in the series :-
The Substrate S1 gives rise to the product S2 through a
reaction controlled by the enzyme E1. S2 now becomes the
substrate of another reaction controlled by the enzyme E2 and
So on.
In the synthesis of different amino acid from aspartate.
Lysine is formed after several steps.
28. It has been found that the addition of lysine stops the whole chain
of reactions. Here inhibition is produced not in that last steps of
the series but in the first steps. Thus Lysine affects the reaction of
an enzyme which is producing an entirely different substance.
This has been explained by suggesting that the enzymes has a
‘Control site in addition to the active site. When the control site is
occupied by a control Substance ( lysine in this case) the letter
distorts the shape of the enzyme .One or more reactive amino
acid are removed from the active site. Which is thus rendered
non functional .Enzyme which undergo this types of behaviors
are called allosteric enzyme. They control an entire series of
reaction through the end product.
29. Conclusion
The Enzyme action mechanism are used to catalyzed
reaction and act as a biocatalyst. (That speed up the
reaction).
The enzyme find many application in our daily life.
The enzymes have vital role in biological system. They
reduce the activation energy of the reactant in such a way
that all the biological systems occur at body temperature
below 40oC.
