Classification of enzymes, factors, importance

1. Enzymes
Maria Gul
lecturer
Johar institute of professional studies

2. enzymes
Catalyst are agent that in minute amount increases the velocity of chemical reaction of other
substance without itself being destroyed or altered upon the completion of reaction.
Enzymes are biological catalyst
Enzymes produce by living cells.
Protein in nature
The substance on which enzyme act called substrate
Enzymes accelerate the chemical reaction but do not initiate
Rx without enzyme can take place bt rate of reaction vl be very slow.

3. Enzymes – are organic catalyst produced by an
organisms. The reactant in an enzyme-catalyzed reaction
is called substrate.substra.

4. The small portion of the molecule that is responsible for
the catalytic action of the enzyme is the active site.active
site”.

5. Enzymes are superior to other catalysts in several
ways:
1. They have a much greater catalytic power.
OVERVIEW of ENZYMES

6. 2. Enzymes are highly specific with varying degrees of specifity.
1.Absolute specifity – they act on one substrate and only on that
substrate.
CO2 + H2O carbonic anhydraseH2CO3
2.Stereospecifity – such enzymes that can detect the difference
between optical isomers (mirror images) and select only one of
such isomers. (Starch______(alpha glucosidase) )
• Cellulase ------beta glycosidic bond.
OVERVIEW of ENZYMES
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7. 3.Group specifity – enzymes that catalyzes a group of
substances that contain specific compounds.
Hexokinase-------glucose,mannose,fructose
Lipase --------lipid
4. Bond specific
Trypsin, chymotrypsin _________peptide
3. The activity of enzymes is closely regulated, whereas the
catalyst is difficult to control.

8. ENZYME SUBTRATE or REACTION TYPE
Maltase Maltose
Urease Urea
Proteases Proteins
Lipases Lipids
Hydrolases Hydrolysis Reaction
Deaminases Removing amines
Dehydrogenases Removing hydrogens
NOMENCLATURE

9. Enzymes are proteins in nature and therefore undergo all the reactions
as proteins do.
• coagulated by heat, alcohol, strong acids, and alkaloidal reagents.
• Isoelectric PH
• On denaturation lose its catalytic activity
4.Temperature Requirement
The higher the temperature, the faster the rate of reaction. The
best temperature for enzyme function – the temperature at which the
rate of a reaction involving an enzyme is the greatest – is called the
“optimum temperature”.

10. 5.Role of pH
Each enzyme has a pH range within which it can
best function. This is called “optimum pH range” for that
particular enzyme. For example, the optimum pH range
of pepsin, an enzyme found in gastric juice, is
approximately 2.0, whereas the optimum pH range of
trypsin, an enzyme found in pancreatic juice, is near 8.2.

11. If the pH of a substrate is too far from the
optimum pH required by the enzyme, that
enzyme cannot function at all. However, since
body fluids contains buffers, the pH usually does
not vary too far from the optimum values.

12. 6.Effect of Concentration
As with the all chemical reactions, the speed is
increased with an increase in concentration of
reacctants. With an increased concentration of
substrate, the rate of the reaction will increase until
available enzyme becomes saturated with substrate.
Also with an increase in the amount of enzyme, the rate of
reaction will increase, assuming an unlimited suppMluhamy omafd Rsamuzabn Usl Rterhmaante.
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13. 7. Direction of enzymes
Reversible
Irreversible
8. Location of Enzymes
Fatty acid synthesis, glycolysis in cytosol
Fatty acid oxidation, tca in Mitochondria

14. Activators – inorganic substances that tend to increase
the activity of enzyme.
Inhibitors – any substance that will make the enzyme
less active or render it inactive.
Competitive inhibitors – binds reversibly in the active site
and so block the access by the substrate.
Incompetitive inhibitors – bind to another site on the
enzyme to render it less active or inactive.
ACTIVATORS and INHIBITORS

15. Irreversible inhibitors – form strong
covalent bonds with the enzymes,
rendering it inactive. This effect can’t be
overcome by increasing the concentration
of the substrate.
ACTIVATORS and INHIBITORS

16. Lock-and key Model
Wherein the substrate must “fit” into the active site of the
enzyme – hence the specifity of the enzyme.
Induced-Fit Model
Suggests that the active site is not rigid as the Lock-and-Key
Model, but flexible. That is, the site changes in conformation upon
binding to a
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17. ZYMOGENS or proenzyme
Zymogens
are inactive pprecursors of enzymes. Most
digestive and blood-clotting enzymes exist in the zymogen
form, until activated.
In the case of digestive enzymes, this is necessary to
prevent digestion of pancreatic and gastric tissue. For
blood clotting, it is to avoid premature of blood cells.

18. ZYMOGENS
ZYMOGEN ACTIVE FORM OF ENZYME
Pepsinogen (363 ) a.a Pepsin (321)
Trypsinogen (229) Trypsin (223)
Chymotrypsinogen chymotrypsin

19. Other enzymes are conjugated proteins – they contain a
protein and non-protein part. Both parts must be present
before the enzyme can function.
The protein part is called the “apoenzyme” and the non-
protein (organic part) is called prosthetic gp
prosthetic gp may be co factor / co-enzyme “coenzyme”.
APOENZYMES and COENZYMES

21. Coenzymes are not proteins part may be organic or metal-organic
molecules. and so are not inactivated by heat. Transfer a specific
gp
Examples of coenzymes are the vitamins or compounds derived
from vitamins. The reaction involving a coenzyme can be written
as follows:
coenzyme + apoenzyme = enzyme
Coenzyme A (pantothenic acid)
NAD, NADH, FAD, FADH, TPP.

22. Isozymes or Isoenzymes
are enzymes with the same organism and function
but slightly different physically and chemically distinct
from each other. The reason for their existence is not
unknown, but they are made use of clinically. Lactate
dehydrogenase ( 5LDH)(energy production), creatine
kinase (3)( energy transport and buffering system) and
all occur in isoenzyme form and are diagnostic value. LDH
has five forms.
ISOZYMES

24. Formerly enzyme were given names ending in
“-in”. With no relation being an indicator between
the enzyme and the substance it affects – the
substrate.
The current system for naming enzymes uses
the name of the substrate or the type of reaction
involved, with the ending “-ase”.

25. Factors affecting Enzyme activity
Enzyme concentration
Substrate concentration
Effect of temperature
Effect of PH
Presence of cofactors, coenzyme.
Presence of inhibitors

27. Transferase
Transfer of specific group (phosphate,
amino ,methyl gp)
Glucose ______hexokinase (glucose -6-
phosphate)
Aminotransferase

28. Hydrolyases
Sucrase
Maltase
Glucose-6-phosphate________H2O___glucose 6 phosphatase___glucose+Pi
ISOMERASE

29. Lyase
Catalyze the cleavage b/w c-c, c-s, c-o

30. Ligase
Catalze the formation of bond b/w carbon and o,s,N
coupled to hydrolysis of high energy phosphate

33. The measurement of plasma enzyme levels can
be of great diagnostic value.
Many other plasma enzymes areuseful in the
diagnosisof various diseases.
CLINICAL SIGNIFICANCE OF PLASMA
ENZYME CONCENTRATIONS

34. Importance

37. Lactose Intolerance
Individuals who cannot eat food
containing lactose are said to be lactose intolerant.
They lack enzyme lactase, which is requires for the
hydrolysis of lactose.
As a result, lactose acuumulates in the
intestinal tract and pulls water out of the tissues by
osmosis. This is turn causes abdominal cramps,
distention, and diarrhea.

38. Lactose Intolerance
To overcome such an effect today, an
individual may take Lactaid orally to supply the
missing enzyme.

40. 40
Effectofsubstrateconcentration
• At lower concentrations, the active sites on most of the
enzyme molecules are not filled because there is not
much substrate.
• Higher concentrations cause more collisions between the
molecules.
• The rate of reaction increases (First order reaction).

41. 41
Effectofsubstrateconcentration(contd.)
• The maximum velocity of a reaction is reached when the
active sites are almost continuously filled.
• Increased substrate concentration after this point will not
increase the rate.
• Reaction rate therefore increases as substrate
concentration is increased but it levels off (Zero order
reaction)

42. Effectofsubstrateconcentration
The shape of the curve
that relates activity to
substrate concentration
is hyperbolic.
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First
order
reaction
Zero order
reaction

43. • At points A or B, increasing or
decreasing [S] therefore will
increase or decrease the
number of ES complexes with a
corresponding change in vi.
• The rate of reaction is
substrate dependent (First
order reaction).
• At point C essentially all the
enzyme is present as the ES
complex. Since no free enzyme
remains available for forming
ES, further increases in [S]
cannot increase the rate of the
reaction .
• Reaction rate therefore
becomes independent of
substrate concentration
(Zero order reaction).
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44. Effectofenzymeconcentration
As the amount of enzyme is
increases the rate of reaction
increases. If there are more
enzyme molecules than are
needed, adding additional enzyme
will not increase the rate. Reaction
rate therefore increases as
enzyme concentration increases
but then it levels off.
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45. Effectofproductconcentration
• The enzyme activity declines when the products start
accumulating. This is called product or feed back inhibition.
• Under certain conditions reverse reaction may be favored
forming back the substrate.
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46. 46
EffectofTemperature
• Raising the temperature increases the kinetic energy of
molecules.
• Increasing the kinetic energy of molecules also increases their
motion and therefore the frequency with which they collide.
• This combination of more frequent and more highly
energetic and productive collisions increases the reaction
rate.

47. 47
Temperaturecoefficient
• The Q10, or temperature coefficient, is the factor by which the
rate of a biologic process increases for a 10 °C increase in
temperature.
• For the temperatures over which enzymes are stable, the
rates of most biologic processes typically double for a 10 °C
rise in temperature (Q10 = 2). (A ten degree Centigrade rise in
temperature will increase the activity of most enzymes by 50
to 100%).

48. EffectofTemperature
• The reaction rate increases with
temperature to a maximum level, then
abruptly declines with further increase
of temperature.
• Most animal enzymes rapidly become
denatured at temperatures above 40oC.
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49. 49
EffectofTemperature
• The optimal temperatures of the enzymes in higher organisms
rarely exceed 50 °C.
• Some enzymes lose their activity when frozen.
• Enzymes from thermophilic bacteria found in hot springs are
active at 100 °C (taq polymerase used in pcr)
• Changes in the rates of enzyme-catalyzed reactions that
accompany a rise or fall in body temperature constitute a
prominent survival feature for "cold-blooded" life forms such as
lizards or fish, whose body temperatures are dictated by the
external environment.

50. EffectofHydrogenIonConcentration(pH)
• The rate of almost all enzyme-
catalyzed reactions exhibits a
significant dependence on hydrogen
ion concentration.
• Most intracellular enzymes exhibit
optimal activity at pH values
between 5 and 9.
• When the activity is plotted against pH,
a bell-shaped curve is usually obtained
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51. EffectofHydrogenIon
Concentration(pH)
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• The pH optimum—i. e., the pH value at
which enzyme activity is at its maximum—is
often close to the pH value of the cells (i. e.,
pH 7).
• There are also exceptions to this.
• The proteinase pepsin , which is active in the
acidic gastric lumen, has a pH optimum of 2,
while alkaline phosphatase is active at pH
values higher than 9

52. Effectof
activatorsand
Coenzymes
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• The activity of certain enzymes is
greatly dependent on metal ion
activators and coenzymes.
• Vitamins act as coenzymes in a variety
of reactions.

53. MICHAELIS-MENTEN EQUATION
Reaction model
Leonor Michaelis and Maude Menten proposed a simple model that
accounts for most of the features of enzyme-catalyzed reactions. In
this model, the enzyme reversibly combines with its substrate to
form an ES complex that subsequently yields product, regenerating
the free enzyme. The model, involving one substrate molecule, is
represented below:
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54. eq
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55. Relative concentrations of E and S: The concentration of substrate
([S]) is much greater than the concentration of enzyme
([E]), so that the percentage of total substrate bound by the
enzyme at any one time is small.
2. Steady-state assumption: [ES] does not change with time (the
steady-state assumption), that is, the rate of formation of ES is equal
to that of the breakdown of ES (to E + S and to E + P). In general, an
intermediate in a series of reactions is said to be in steadystate
when its rate of synthesis is equal to its rate of degradation.
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56. Initial velocity: Initial reaction velocities (vo) are used in the analysis
of enzyme reactions. This means that the rate of the reaction is
measured as soon as enzyme and substrate are mixed. At that
time, the concentration of product is very small and, therefore, the
rate of the back reaction from P to S can be ignored.
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57. C. Important conclusions about Michaelis-Menten kinetics
1. Characteristics of Km: Km—the Michaelis constant—is characteristic
of an enzyme and its particular substrate, and reflects the
affinity of the enzyme for that substrate. Km is numerically equal to
the substrate concentration at which the reaction velocity is equal
to 1⁄2Vmax. Km does not vary with the concentration of enzyme.
a. Small Km: A numerically small (low) Km reflects a high affinity of
the enzyme for substrate, because a low concentration of substrate
is needed to half-saturate the enzyme—that is, to reach a
velocity that is 1⁄2Vmax (Figure 5.9).
b. Large Km: A numerically large (high) Km reflects a low affinity
of enzyme for substrate because a high concentration of substrate
is needed to half-saturate the enzyme.
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58. 2. Relationship of velocity to enzyme concentration: The rate of the
reaction is directly proportional to the enzyme concentration at all
substrate concentrations. For example, if the enzyme concentration is
halved, the initial rate of the reaction (vo), as well as that of Vmax, are
reduced to half that of the original.
3. Order of reaction: When [S] is much less than Km, the velocity of the
reaction is approximately proportional to the substrate concentration. The
rate of reaction is then said to be
first order with respect to substrate. When [S] is much greater
than Km, the velocity is constant and equal to Vmax. The rate of
reaction is then independent of substrate concentration, and is
said to be zero order with respect to substrate concentration
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59. figure
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60. Figure
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61. Double reciprocal plot
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62. INHIBITION OF ENZYME ACTIVITY
Any substance that can diminish the velocity of an enzyme-catalyzed
reaction is called an inhibitor. In general, irreversible inhibitors bind to
enzymes through covalent bonds. Reversible inhibitors typically bind to
enzymes through noncovalent bonds, thus dilution of the
enzyme–inhibitor complex results in dissociation of the reversibly
bound inhibitor, and recovery of enzyme activity. The two most commonly
encountered types of reversible inhibition are competitive and
noncompetitive.
A. Competitive inhibition
This type of inhibition occurs when the inhibitor binds reversibly to
the same site that the substrate would normally occupy and, therefore,
competes with the substrate for that site.
Statin drugs as examples of competitive inhibitors. atorvastatin (Lipitor) and pravastatin 62

63. Noncompetitive inhibition
This type of inhibition is recognized by its characteristic effect on Vmax
Noncompetitive inhibition occurs when the inhibitor and
substrate bind at different sites on the enzyme. The noncompetitive
inhibitor can bind either free enzyme or the ES complex, thereby preventing
the reaction from occurring.
noncompetitive inhibition are certain insecticides, whose neurotoxic effects are a result of their
covalent binding at the catalytic site of the enzyme acetylcholinesterase (an enzyme that cleaves
the neurotransmitter, acetylcholine).
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