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 be Physical like size shape and :
Chemical like nature of the molecules Proteins, CHOs , Lipids and Nucleic acids

3. The properties of enzymes
The nature of the enzymes
Activation energy and active site
Catalytic efficiency and Enzyme specificity
Regulation of enzyme activity
Distribution/location of enzyme
Site of synthesis and action
Quantity of enzymes – Intra/Extra cellular

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 rRNA- Ribozymes
So is the Creatine Kinase (CK)
rRNA establish peptide bond B/W the Amino acids of the Product proteins – Releases energy

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
(E and S) bind for ESC and transformed into Products
It is much lower than required for the non catalyzed reactions
online.org

6. Active site – Has Amino Acyl groups binding and catalytic part
Active sites are the pockets/hollows on the surface of E that assume 3D shape after protein folding
Active site contains the side chains of the AAs (amino Acyl or functional groups) of the enzyme
Only AAs are involved in the Substrate binding and Catalysis
Has 2 sites for 1. substrate binding and 2. catalysis
Enzyme chooses S, binds it to active site and catalyzed for products
cell- ncbibookshelf.gov

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 S are transformed into products / unit time
Turnover number is the maximum no: of substrates converted to products/ active site/ unit time (Minutes)
Turn over no: of Carbonic Anhydrase is 36million/active site/minute
dictionary.com

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 Like:
ketogenesis in liver mitochondria and ketolysis in extra hepatic tissues

10. Regulation of enzyme activity
Cell regulates enzyme activity according to their requirements through enzyme activation or inhibition
Cell controls the rate of enzyme forward and reverse reaction
Glycogen Synthase is active when there is excess of glucose (fed state) and body needs to store CHOs as Glycogen
Its activity is inhibited when there is hypoglycemia

11. Distribution/Location of enzymes Intra/Extra cellular
Majority of the E are intracellular except digestive enzymes which are present in the lumen of GIT (Pepsin and trypsin)
Enzymes are also localized in the specific organelles called compartmentalization like Mitochondria
It house the enzymes for FA oxidation and Citric acid cycle and

12. Location of enzymes cont. provide favorable environment
Cytosole has the enzymes for Glycolysis, Fatty acid synthesis and HMP pathway
Lysosomes contain Acid Hydrolases to degrade macro moles: Proteins; Glycogen,TG and Nucleic acids
Localization provides favorable environment for catalyzation
Acid Hydrolases work best at pH 5 in Lysosome and
Intestinal/ Pancreatic enzymes at alkaline pH 8

13. Site of synthesis/action reused and measured
The site of synthesis and action of enzymes is the same
A small amount of E is required for catalysis
Enzymes are not consumed can be reused
Enzymes can be measured for diagnosis and:
Follow up for the treatment

14. 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.
Like: 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 like:
Pepsin and Trypsin that catalyze the proteins into AAs in GIT

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

16. Classification of enzymes - Reaction types

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

18. Theories /models of enzyme action. 3
There are 3 theories about enzyme action depending upon: Flexibility or rigidity of the Active site
2. Changes in the shape of the Enzymes, substrate and active
site after binding
1.Lock and Key Theory
2. Induced – fit theory and
3. Transition – State Model/Theory

19. Lock and key theory/Model active site is rigid
The lock-and-key theory explains that Active site is rigid
E /active site accommodate substrates, having specific shapes , sizes and functional groups
So only specific substances fit in an active site to form ESC
Rigidity of active site is its limitation but research suggest that enzyme/active site is not so rigid but flexible

20. Lock and Key theory

21. Induced fit model/theory E/active site changes to S
This model is the more accepted for enzyme action than the lock-and-key model.
It states that enzymes are rather flexible structures in which the active site continually reshapes itself
The active site interacts with the substrate until the substrate is completely bound to it. ( final shape of enzyme is achieved) 
(E/active site changes itself to accommodate substrate)

22. Induced fit model

23. Transition- state Theory - TST S alters 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

24. Transition state theory