Enzymes in biochemistry

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

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
9/10/2014 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 2

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4. 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
9/10/2014 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 4

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
9/10/2014 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 5

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
9/10/2014 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 6

7. Apo-enzyme + Coenzyme Holo-enzyme
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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
9/10/2014 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 8

9. Coenzymes may be divided in to two groups
First group
• Coenzymes taking part in reactions catalyzed by oxidoreductases by
donating or accepting hydrogen atom or electron
• These coenzymes can be considered as co-substrates
• Changes occurring in the substrate is counterbalanced by the
co-enzyme
9/10/2014 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 9

10. • Two hydrogens are removed from lactate
Two electrons and one hydrogen are accepted by NAD+ to
form NADH
Remaining H+ is released to the surrounding
Coenzyme transferring hydrogen
• NAD+, NADP+
9/10/2014 • FMNDr. A,sh oFk AKumDar J; Professor; Department of Biochemistry. 10

11. Second group
• Coenzymes taking part in transferring groups other than hydrogen
Alanine αKetoglutarate
Transaminase (amino transferase)
Pyridoxal phosphate (PLP)
Pyruvate Glutamate
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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
9/10/2014 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 12

13. • Once the reaction is completed – coenzyme is released from the apo-enzyme
• Can bind to another enzyme molecule
Glyceraldehyde-
3- phosphate
NAD+
NADH+H+
1,3 bisphosphoglycerate
Lactate Pyruvate
9/10/2014 Dr. Ashok Kumar J; Professor; Department of Biochemistry. 13

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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16. Enzyme activity depends upon
Three dimensional (3D) structure of the
enzyme protein
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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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22. S
+ S P P
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26. Thank you
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