This presentation helps to understand about structure of enzyme and mechanism of action.

1. Enzyme Structure and Mechanism of Action
Prepared by : Mrs. Swati Raysing
Assistant professor (Quality Assurance)
R.C.Patel Institute of Pharmaceutical Education and Research,
Shirpur, Dhule, Maharashtra

2. Define enzymes
(Enzymes as Biological Catalysts)
• Enzymes are specialized proteins that increase the rate of reaction by
lowering the energy of activation
• They catalyze nearly all the chemical reactions taking place in the cells
of the body.
• The catalytic behaviour of any protein enzyme is dependent on the
primary, secondary, tertiary and quaternary structure of the protein
molecule.

3. Importance
• Enzymes play an important role in Metabolism, Diagnosis, and
Therapeutics.
• All biochemical reactions are enzyme catalyzed in the living
organism.
• Level of enzyme in blood are of diagnostic importance e.g. it is a good
indicator in disease such as myocardial infarction.
• Enzyme can be used therapeutically such as digestive enzymes.

4. Important Terms to Understand Biochemical Nature
And Activity of Enzymes
• Active site:
The area on the enzyme where the substrate or substrates attach to is
called the active site.
• Enzymes are usually very large proteins and the active site is just a
small region of the enzyme molecule.
• Enzyme molecules contain a special pocket or cleft called the active
sites.

5. • APOENZYME and HOLOENZYME
• The enzyme without its non protein moiety is termed as apoenzyme
and it is inactive.
• Holoenzyme is an active enzyme with its non protein component.

6. • Cofactor:
• A cofactor is a non-protein chemical compound that is bound (either tightly
or loosely) to an enzyme and is required for catalysis.
• Types of Cofactors:
Coenzyme: The non-protein component, loosely bound to apoenzyme by
non-covalent bond.
• Examples : vitamins or compound derived from vitamins.
Prosthetic group :
The non-protein component, tightly bound to the apoenzyme by covalent
bonds is called a Prosthetic group.

7. Intracellular and extracellular enzymes
Intracellular
• Enzymes are synthesized and retained in the cell for the use of cell
itself.
• They are found in the cytoplasm, nucleus, mitochondria and
chloroplast.
• Example: Oxidoreductase catalyses biological oxidation, Enzymes
involved in reduction in the mitochondria.
Extracellular
• Enzymes are synthesized in the cell but secreted from the cell to work
externally.
• Example : Digestive enzyme produced by the pancreas, are not used
by the cells in the pancreas but are transported to the duodenum.

8. Enzyme Nomenclature
Traditionally, enzymes often were named by adding the suffix –ase to the
substrate upon which they acted
Ex: phosphatase, urease, catalase, proteases
Confusion arose from these trivial naming.
So a new system of nomenclature of enzyme was developed based on
nature of reaction it helps
Six classes of reactions are recognized
–Within each class are subclasses, and under each subclass are sub subclasses
within which individual enzymes are listed

9. Classification of Enzyme
Enzyme are classified on the basis of action it performs
1. Oxidoreductases -oxidation–reduction reactions
Phosphate dehydrogenase
2. Transferases-transfer of functional groups
Methyltransferases, Carboxyltransferases
3. Hydrolases-hydrolysis reactions
Carboxylic ester hydrolases

10. Classification of Enzyme
4. Isomerases-isomerizationreactions
Epimerases
5. Lyases-addition to double bonds
Carboxylyases, Aldehydelyases
6. Ligases-formation of bonds with ATP cleavage
Amino acid–RNA ligases

11. Chemical Properties
• Most of enzymes carry out their functions relying solely on their protein
structure
• Many others require non-protein components – cofactors
– Usually metal ion or non-protein organic part (Coenzyme)
• Less complex than proteins, tend to be stable to heat
• Many coenzymes are vitamins or contain vitamins as part of their
structure

12. Chemical Properties
• If the enzyme is made of single polypeptide – monomeric enzyme.
Ex: ribonuclease, trypsin
• If the enzyme is made up of more than one polypeptide – oligomeric
enzyme. Ex: lactate dehydrogenase, aspartate transcarbamoylase
• Multienzyme complex: have multiple enzyme unit to carry out
different reaction in sequence

13. Factors effecting enzyme activity
• The contact between enzyme and substrate is the most essential pre-requisite for
enzyme activity.
• The important factors that influence the enzyme reaction are:
1. Concentration of Substrate
2. Concentration of Enzyme
3. Temperature
4. pH
5. Product concentration
6. Activators
7. Time
8. Light and radiation

14. Substrate Concentration and Reaction Rate
• The rate of reaction increases as substrate concentration increases (at
constant enzyme concentration)
• Maximum activity occurs when the enzyme is saturated (when all
enzymes are binding substrate)

15. • Concentration of Enzyme : Reaction velocity is directly proportional
to concentration of enzyme.
• Temperature :
• Optimum temperature The temp at which enzymatic reaction occur
fastest.

16. pH
• Most intracellular enzymes exhibit optimal activity at pH values
between 6 - 8.
• Balance between enzyme denaturation at high or low pH and effects
on the charged state of the enzyme, the substrates, or both
• Exception – pepsin (1-2), acid phosphatase (4-5), alkaline phophatase
(10-11)

17. Activators
Certain metallica cations – Mn, Mg, Zn, Ca, Co, Cu, Na, K.
It acts in a various ways
– Combining with substrate
– Formation of E-S metal complex, direct participation in the reaction and bringing a
conformational changes in enzyme
There are 2 categories of enzyme requiring metals for their activity
Metal activated enzyme:Not tightly held by the enzyme and can be exchanged easily. Ex:
ATPAase (Mg and Ca) and Enolase
Metalloenzyme: Hold the metal tightly. Ex: alcohol dehydrogenase, carbonic anhydrase,
alkaline phosphatase, carboxypeptidase

18. Other Factor
• Product concentration: Accumulation of reaction products generally
decreases the enzyme velocity
• Light and radiation: exposure to UV, betagamma and X-rays
inactivates certain enzyme
– Formation of peroxides, ex: UV rays inhibit salivary amylase activity

19. Mechanism of Action of Enzymes
• Enzymes increase reaction rates by decreasing the Activation energy:
• Enzyme-Substrate Interactions:
‒Formation of Enzyme substrate complex by:
1. Lock-and-Key Model
2. Induced Fit Model

20. Lock-and-Key Model
• In the lock-and-key model of enzyme action:
- the active site has a rigid shape
- only substrates with the matching shape can fit
- the substrate is a key that fits the lock of the active site
• This is an older model, however, and does not work for all enzymes

21. Induced Fit Model
• In the induced-fit model of enzyme action:
 - the active site is flexible, not rigid
 - the shapes of the enzyme, active site, and substrate adjust to
maximumize the fit, which improves catalysis
 - there is a greater range of substrate specificity
• This model is more consistent with a wider range of enzymes