1. Enzymes-2 – Properties, classification and theories of action lecture NO : 1st MBBs
Dr Muhammad Ramzan

2. Properties – the definition
Any measureable aspect of the system that is essential to maintain the material structure of life
The property can Physical like size shape and :
Chemical like nature of the molecule Protein CHO, Lipids and Nucleic acid

3. The properties of enzymes
Followings are the enzymes‘ properties
The nature .
Activation energy and Active site
Catalytic efficiency and Enzyme specificity
Regulation of enzyme activity
Distribution/location of enzyme
Site of synthesis and action

4. Nature of the Enzymes
All the enzymes are proteins that ↑ the velocity of a chemical reaction and are not consumed during the reaction
Some of the RNAs also act as enzymes like rRNAs- Ribozymes that are involved in protein synthesis
These RNAs establish peptide bond B/W the Amino acids of the Product proteins

5. Activation energy
It is the minimum amount of energy required to Initiate and complete a catalyzed chemical reaction
Enzymes reduce the activation energy to make the reactants
(Enzyme and Substrate) to bind for ESC :
and transformed into Products
It is much lower than required for the non catalyzed reactions

6. Active site – Has functional/Amino Acyl groups (2-4 AAs)
Active sites are the pockets/hollows on the surface of E that assumes 3D shape after protein folding
Active site contains the side chains of the AAs (amino Acyl or functional groups AAs) that are involved in the :
Substrate binding and Catalysis
Binding of S to active site produces ESC which is cleaved to products and enzyme .
Both are released and enzyme can be reused

7. Active site

8. Catalytic efficiency
Es are the efficient catalysts and can ↑ the rate of chemical reaction up to 103 to 108 than the uncatalysed reaction
About 100 to 1000 substrates are transformed into the products / unit time
Turnover number is the maximum no: of substrates converted into products/ active site/ unit time
Turn over no: of Carbonic Anhydrase is 36million/active site/minute

9. Enzyme specificity
Enzymes are highly specific and interact with specific substrates with specific functional groups
Other substrates would not fit into their active sites
It catalyzes only one type of chemical reaction
The set of enzymes present in a cell determines which type of reaction will occur in that cell

10. Cofactors - property of enzymes non protein parts of E
Cofactors are the non protein components of an enzyme and is essential for E activity
Halozyme is an active enzyme with protein and a cofactor
There are 2 types of cofactors that bind to the active site
Inorganic metallic ions : like Iron, Magnesium and Zinc.
Also called as Co factors
Organic molecules: like Co A; NAD,NADH and FAD
Also called as Coenzymes

11. Regulation of enzyme activity
Enzyme activity can be regulated
Cell regulates the activity of the enzyme according to their demand and need through E activation or inhibition
Like Glycogen Synthase is active when there is excess of glucose and body needs to store CHOs as Glycogen
Its activity is inhibited when there is hypoglycemia

12. Distribution/Location of enzymes 1 Intra/Extra cellular
Majority of the E are intracellular except digestive enzymes which are present in the lumen of GIT
Enzymes are also localized in the specific organelles called compartmentalization like Mitochondria that :
House the enzymes for FA oxidation and Citric acid cycle
Intra cellular Es are secreted in small and Extra cellar in large quantities

13. Location of enzymes 2
Cytosole has the enzymes for Glycolysis, Fatty acid synthesis and HMP pathway
Lysosomes contain the enzymes (Hydrolases) for the :
Degradation of macromolecules like TG; Proteins, Glycogen and Nucleic acids
Compartmentalization provides the favorable environment for the reactions to occur

14. Site of synthesis/action reused and measured
The site of synthesis and action is the same
A small amount of E is required for catalysis
Enzymes can be reused and measured for diagnostic and monitoring (treatment) purposes

15. Classification of enzyme – by adding suffix - "ase"
Es are commonly named by adding the suffix "-ase" to the root name of the substrate molecule it is acting upon.
For example, Lipase catalyzes the hydrolysis of lipids/TG
Sucrase catalyzes the sucrose into Glucose and fructose
A few enzymes discovered before this naming system are known by their common names
Examples are the Pepsin and Trypsin which catalyze the proteins .AAs

16. Classification of enzymes – IEC Based upon type of reaction
The latest systematic nomenclature system known as the International Enzyme Commission (IEC) system
is based upon the type of reaction catalyzed.
There are six broad groups of enzymes in this system

17. Classification of enzymes - Reaction types

18. Enzyme action – theories or Models Active site is common to all E
Enzymes differ widely in structure and specificity, but a general theory that accounts for their catalytic behavior
is widely accepted. Like :
The enzyme and its substrates interact only over a small region over the surface of the enzyme
called the Active site.

19. Theories /models of enzyme action. 3
There are 3 theories about mechanism of E action with minor difference of the flexibility or rigidity of the Active site and changes in the conformation/shape of :
Enzyme, substrate and active site
Lock and key Theory
Induced – fit theory
The Transition – State Model/Theory

20. Lock and key theory
The lock-and-key theory explains the high specificity of E activity.
- Enzyme surfaces accommodate substrates, having specific shapes , sizes and functional groups
So only specific substances ― fit in an active site to form
a ES complex.

21. Limitation of Lock and key theory Rigid E conformation
A limitation of this theory is that it requires enzymes
conformations to be rigid and so is the (active site)
Research suggests that enzymes conformations are not so rigid but some what flexible.

22. Enzyme – Lock and key model

23. Induced fit model/theory E/active site changes to S
This model is the more accepted for enzyme-substrate complex than the lock-and-key model.
It shows that enzymes are rather flexible structures in which the active site continually reshapes by:
Its interaction with the substrate until the substrate is completely bound to it.
Which is also the point at which the final form and shape of the enzyme is determined.

24. Enzyme – Induced – fit model

25. Transition- state Theory - TST S to activated Complex
Transition state theory begins with binding of the Substrate to the active site of the enzyme
There is a change in the Geometry of the S after E binding to assume a state that is neither a product nor ESC
This transition/activated complex undergoes catalysis to products
The demerit is the high cast of energy

26. Transition state Model/Theory -TST

27. Transition state/activated state theory