The document discusses various modes of regulating enzyme activity, including allosteric regulation, covalent modification, induction and repression, compartmentalization, and isoenzymes. Allosteric regulation involves effector molecules binding at allosteric sites and inducing conformational changes that increase or decrease the enzyme's activity. Covalent modification can activate or inactivate enzymes through additions like phosphorylation. Induction and repression alter the amount of enzyme by increasing or decreasing its synthesis in response to signals. Compartmentalization separates pathways to increase efficiency, while isoenzymes form multienzyme complexes for the same purpose.

1. Regulation of enzyme
activity
Dr. Ashok Kumar. J.
International Medical School
Management and Science University
Malaysia
9/10/2014 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 1

2. OBJECTIVES: To learn……
• Enzyme specificity
• Importance of regulation of enzyme activity
• Different modes of regulation of enzyme activity
• Allosteric regulation
• Covalent modification
• Induction and repression
• Compartmentalization
• Isoenzymes
9/10/2014 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 2

3. 9/10/2014 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 3

4. 2. Stereospecificity
Show specificity towards one steroisomeric form of the
substrate
e. g. : L- Lactate dehydrogenase can act only on L-lactate
D- Amino acid oxidase can act only on
D- amino acid not on L- amino acid
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5. 3. Bond specificity Group Specificity
Proteolytic enzymes show bond specificity
Hydrolyze specific bond with a specific side chain group
Proteolytic enzymes :- Enzymes involved in hydrolyzing peptide bond
e.g.: Trypsin : hydrolyze peptide bond formed by
carboxyl group of arginine or lysine
Chemotrypsin : hydrolyze peptide bond
formed by the carboxyl group of
aromatic amino acids
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6. 4. Group specificity
Same enzyme catalyze the same reaction on a group of
structurally similar compounds
e.g: Hexokinase
Catalyzes phosphorylation of glucose, galactose, mannose
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7. Regulation of enzyme activity
Importance regulation of enzyme activity
Regulation of by
Allosteric regulation
Covalent Modification (reversible and irreversible)
Induction and repression
compartmentalization
Isoenzymes
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8. Importance
• Helps to use the substrate economically
• Regulate the metabolic pathways and their interrelations
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9. Allostearic “occupying another space”
Allosteric site was first proposed by
Jacques Monod
Substances which bind to allostearic site can
modify their activity – Allosteric effector
Allosteric effectors
Substances that bind to allosteric site and
modifies the activity of the protein
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10. Binding of an allosteric effector induces
conformational change in the enzyme
Allosteric activator and inhibitor exhibit positive
and negative cooperativities with the substrate
Allosteric activator :-
on binding to the allosteric site promote
binding of substrate to the acive site or the
catalytic action
Allosteric inhibitor:- has opposite action
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Dr. Ashok Kumar J; Professor; Department of Biochemistry.

11. Allosteric enzymes possessing more than one substrate
binding site on its subunits can bind many substrates
Binding of one substrate to active site increases the affinity of
other active site to substrate
Homotropic effect
Allosteric modulator is different from the substrate
Heterotropic allosteric effect
9/10/2014 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 11

12. According to heterotropic effect of
allosteric modulators
Allosteric enzymes are classified into
1. K series enzymes
2. V series (M series) enzymes
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13. K – class of allosteric enzymes
• Allosteric effector changes the Km of the
enzyme, Vmax is not altered
• Double reciprocal plot is similar to
competitive inhibition
E.g.: Phosphofructokinase
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14. V – class of allosteric enzymes
• Allosteric effector changes the Vmax of
the enzyme, Km is not altered
• Double reciprocal plot is similar to
non-competitive inhibition
E.g.: Acetyl CoA carboxylase
9/10/2014 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 14

15. According to the model used (concerted
model) to study allosteric enzymes –
they exists in two conformational states:
T (tense) and R (relaxed) state
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16. •Allosteric activator favour ‘R’
state of the enzyme
•Allosteric inhibitors favour ‘T’
state of the enzyme
In the absence of the allosteric
modulator an allosteric enzyme
follows the hyperbolic kinetics
R = Relax
(active)
S
X
T = Tense
9/10/2014 (inactive) Dr. Ashok Kumar J; Professor; Department of Biochemistry. 16

17. In the presence of the allosteric inhibitor an
allosteric enzyme follows the sigmoid kinetics
Cooperative
(Sigmoidal)
Noncooperative
(Hyperbolic)
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18. An intermediate or a product of a metabolic
pathway allosterically inhibits an enzyme
catalyzing earlier step
Feed back Allosteric Inhibition
E1 E2 E3 E4 E5 E6
A  B  C  D  E  F  G
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19. CO2 + Glutamine + ATP
Carbamoyl phosphate
Carbamoyl
phosphate
synthetase II
Aspartate
Trans
carbamoylase
Carbamoyl aspartic acid
Aspartate
Transcarbamoylase
Initial step of pathway
which synthesize CTP
CTP acts as allosteric
inhibitor
CTP
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20. Feedback inhibition
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21. 9/10/2014
ALA Synthase
-
Dr. Ashok Kumar J; Professor; Department of
Biochemistry.
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Glycine + Succinyl CoA
δ aminolevulonic acid (ALA)
HEME
ALA Synthase
catalyzes fist step of
heme biosynthesis
Heme end product of
the pathway act as
allosteric inhibitor

22. Feed forward allosteric activation
An intermediate of the pathway act as allosteric
activator of the enzyme catalyzing later step in
that pathway
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23. Addition of a group or removal of a group from
enzyme protein forming covalent bond
Phosphorylation, dephosphorylation
methylation, ADP ribosylation etc
Zymogen activation
Phosphorylation of enzyme proteins can
activate or inactivate the enzyme
Phosphate group is attached to Serine,
Threonine or tyrosine residues
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24. e.g. : enzymes involved in the
metabolism of glycogen
Metabolism of glycogen takes place in
cytosol
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25. Glycogen synthase - Active
(Glycogen Synthesis)
Glycogen Phosphorylase - Inactive
(Glycogen breakdown)
Glycogen synthase - Inactive
(Glycogen Synthesis) P
Glycogen Phosphorylase - Active
(Glycogen breakdown) P
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26. Zymogen activation
(Activation of latent enzyme)
Irreversible covalent modification
Pepsinogen
Pepsin
Trypsinogen
Trypsin
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27. Affect the amount of enzyme present
Increase in synthesis – Induction
Decrease in synthesis - Repression
Inducer
Repressor
Amount of enzyme directly controls the
velocity of the reaction
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28. Constitutive enzymes : Level of which is fairly
constant
Adaptive enzymes : Concentration increases
or decreases as per the need of the body
Alteration in enzyme levels as a result of
induction and repression of enzyme protein
synthesis are slow (Hours to days)
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29. Hormone insulin:
Induces synthesis of –
Glucokinase, phosphofructokinase, Pyruvate
kinase
Represses Synthesis of –
Pyruvate carboxylase, Phosphoenol pyruvate
carboxykinase (PEPCK), Glucose 6 phosphatase
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30. Hormone Glucagon, Glucocorticoids and epinephrin
Induces synthesis of –
Pyruvate carboxylase, Phosphoenol pyruvate
carboxykinase (PEPCK), Glucose 6 phosphatase
Glucagon Represses Synthesis of –
Glucokinase, phosphofructokinase, Pyruvate kinase
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31. Compartmentalization
Fatty acid synthesis takesplace in cytosol
Fatty acid oxidation takes place in mitochondria
Synthetic and catabolic pathways located in different
subcellular sites to achieve maximum economy
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32. Isoenzymes
Multienzyme complexes
Increases the efficiency of the metabolic pathway
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33. Thank you
9/10/2014 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 33