Enzyme introduction By Dr. Ashok Kumar J
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04/13/2023 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 1
Introduction to enzymeDr. Ashok Kumar. J.
International Medical SchoolManagement Science University
Malaysia
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04/13/2023 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 2
Objectives: To learn…….
• What are enzymes?• How Catalysts function ?• Coenzymes and their importance• Substrates and enzyme substrate complex• Active site and its characteristics• Free energy of activation • Why enzymes increase the rate of the reaction
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04/13/2023 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 3
ENZYMEProtein in nature
Themolabile
Increase the speed of the reaction
Biocatalysts
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04/13/2023 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 4
CATALYSTS
Bind to substances form highly reactive and
unstable intermediate
Remain unchanged in mass and form on completion of the reaction they catalyze
Small amount of catalyst may be repeatedly used to increase the speed of the reaction
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04/13/2023 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 5
Cannot initiate any reaction that does not
occur spontaneously
Equilibrium constant of the reaction is not altered, but helps to attain it faster
Catalyze the reaction by decreasing the activation energy
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04/13/2023 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 6
Coenzymes Enzyme proteins may be • simple proteins
or • conjugated proteins
Non protein part of the enzyme protein is called cofactor
• Organic molecule - it is called coenzyme• Inorganic (metal) ion metal – frequently termed cofactor
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04/13/2023 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 7
Apo-enzyme + Coenzyme = Holo-enzyme
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04/13/2023 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 8
Coenzymes
Small organic molecules
Derivatives of B complex vitamin
Bind loosely and transiently
If they bind tightly and permanently associated with the enzyme it is called prosthetic group
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04/13/2023 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 9
Coenzymes may be divided in to two groupsFirst group• Coenzymes taking part in reactions catalyzed by oxidoreductases by
donating or accepting hydrogen atom or electron
e.g. Lactate dehydrogenase
Lactate Pyruvate
NAD+ NADH+H+
• These coenzymes can be considered as co-substrates• Changes occurring in the substrate is counterbalanced by the
co-enzyme
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04/13/2023 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 10
e.g. Lactate dehydrogenase
Lactate Pyruvate
NAD+ NADH+H+
• Two hydrogens are removed from lactateTwo electrons and one hydrogen are accepted by NAD+ to
form NADH Remaining H+ is released to the surrounding
Coenzyme transferring hydrogen • NAD+, NADP+• FMN, FAD
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04/13/2023 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 11
Second group• Coenzymes taking part in transferring groups other than hydrogen
Alanine αKetoglutarate
Pyruvate Glutamate
Transaminase (amino transferase)Pyridoxal phosphate (PLP)
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04/13/2023 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 12
Coenzyme • Pyridoxal Phosphate• Thiamine pyrophosphate (TPP)• Biotin• Coenzyme A• Tetrahydrofolate
Group transferred• Amino group• Hydroxy ethyl group• Carbon dioxide• Acyl group• One carbon group
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04/13/2023 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 13
• Once the reaction is completed – coenzyme is released from the apo-enzyme• Can bind to another enzyme molecule
Lactate dehydrogenase
Glyceraldehyde- 3- phosphate
NAD+NADH+H+
Lactate Pyruvate
1,3 bisphosphoglycerate
Glyceraldehyde-3-phosphate dehydrogenase
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04/13/2023 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 14
Cofactors
Non-protein moiety it is called cofactor if it is a metal ion such as Zn2+ , Mg 2+, Cu2+, Mn2+ or Fe2+
Metal activated enzymes: Loose and easily dissociable complex with
specific metal
Metalloenzymes:Higher affinity for specific metals; holds
the metal tightly in the molecules
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04/13/2023 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 15
SUBSTRATE
Substance on which enzyme acts is called substrate
Substrate binds to enzyme at a specific site on the enzyme
Forms Enzyme substrate-complex
Substrate is modified to product
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Enzyme activity depends upon Three dimensional (3D) structure of the enzyme protein
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04/13/2023 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 17
Enzymes are the most specific catalyst known
Tertiary structure of the enzyme folded in such a way as to create a region that has
- correct molecular dimensions- appropriate topology- optimum alignment of counter ion
groups and hydrophobic regions to accommodate a specific substrate
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04/13/2023 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 18
Active site
Is due to tertiary structure of protein Are regarded as clefts or cervices Is not rigid it is flexible Generally has a substrate binding site and a
catalytic site Coenzymes or cofactors on which some enzymes depend are part of the active site
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04/13/2023 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 19
Substrate binds to active site by forming weak non-covalent bonds Of the 20 amino acids, some of them are repeatedly found in active site
e.g. cysteine, serine, aspartate, histidine, lysine, arginine, glutamate, tyrosine
• Enzymes are larger in size compared to substrates
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04/13/2023 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 20
SO ENZYME ACTIVITY DEPENDS ON
pH temperature ionic strength
binding of specific substance to enzyme
?
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04/13/2023 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 21
ENZYME SUBSTRTAE COMPLEX
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+ S P P
Lock and Key ModelFischer’s Template Model
• Active site is pre-shaped • Rigid• Does not explains allostearic modulation
S
EE E
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04/13/2023 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 23
• Flexible• Explains allostearic modulation, competitive inhibition• Accepted
Koshland’s Induced Fit Model
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04/13/2023 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 24
All reactions have an energy barrier separating the reactants and the products
‘Free energy of activation’
Energy difference between the energy of the reactants and high energy intermediates
(transition state) that occur during formation of product
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Thank you