1. Enzymes-1 – Structure and Isoenzymes lecture NO : 1st MBBs
Dr Muhammad Ramzan

2. Enzyme (E) – the definition
A protein that catalyzes chemical reactions of other substances
without itself being consumed or altered upon the:
Completion of the reactions.
Enzymes lower the activation energy
Enzymes are produced by the living organisms
online.gov

3. Enzymes (E) – the background Intra/extra cellular
All Es are proteins except a few catalytic RNAs- Ribozymes + CK
Defect or deficiency of an E produces diseases called "inborn error of metabolism.“ like Lactose Intolerance
Human body contains about 10,000 different enzymes
Some Es work within the cell ( RNA polymerase) and some outside the cells like digestive enzymes (Pepsin and Trypsin)
The substance acted upon by an E is called a Substrate – S

4. Lactose intolerance

5. Biological significance of Enzymes Reduces activation energy
At body temperature, very few biochemical reactions proceed at a significant rate without the presence of an E
Es lower the activation energy of a catalyzed reaction, thus
increasing the rate of the reaction
They do so in a step by step, highly efficient and safe manner 3
Activation energy is the minimum energy, required to start and complete a reaction

6. Enzyme lowers the activation energy

7. Parts of Enzymes(E) - 2 parts body and active site
Enzymes are commonly proteins and variable in size
Each enzyme has a specific area to bind the substrate by the non covalently/temporary bonds
Essentially enzymes have 2 parts:
Body of enzyme and
Active site

8. Structure of enzyme – 2 parts Body and active site

9. Body of enzyme 1 Globular and variable in size
Es are globular proteins and their AA content vary from 62 to 2500 AA residues ( Fatty acid Synthase. FAS )
Es are larger than S and some are grouped together to form enzyme complex like FAS/LDH - 6/4 units
Es are long linear chains of AAs but their activities are due to their 3D Tertiary structures
Apozyme is the inactive enzyme with protein portion only
Holozyme is an active enzyme = protein and cofactor/coenzyme

10. Structure of enzyme Apozyme and Halonzyme

11. Active site of enzyme 2 Produced by protein folding
Active sites are the hollows/cracks/ pockets on the surface of E and are produced by protein folding
Active site assumes 3D structure
Active site has 2- 4 AAs that are involved directly in Substrate binding and catalysis
S binding and catalysis is also due to the electrical and chemical properties of side chains of the AA (+ and – ive)

12. Active site cont. mechanism
This binding is temporary by non covalent bonds
It is relieved after the completion of the catalysis
The binding/catalysis is due to the Amino Acyl or functional groups of the AAs involved
Both, the S and AAs of the active site have the compatible functional groups, sequence of AAs and shape
The usual analogy for this is a key fitting exactly into the lock

13. Active site – the chemistry

14. Cofactor A substance other than substrate
Cofactors are non protein inorganic substances, needed to activate the Es to carry out a specific catalysis
Bind to active site of E like Zinc to Carbonic anhydrase
Fe2+/Fe3+ Cytochromes (ETC) / and HB (Fe3)
K+ and Mg++ to Pyruvate Phosphokinase
They are called helper molecules as they assist the enzymes to carry out catalysis
on line.org – www

15. Co enzymes
Coenzymes are the organic compounds that help the enzyme in catalyzing a chemical reaction
They are usually water soluble vitamins like : NAD,NADH and
FAD for the transfer of O2 and H2
Acetyl COA for the transfer of functional groups like Acyl group
They bind to the active site of enzyme for activation and act as carrier of intermediate products
online.org

16. Enzymes - Principle of working E identifies and binds S
Enzyme identifies the Substrate and binds it to E active site.
Enzyme holds the substrate in a particular Geometric position and forms enzyme substrate complex (ESC)
This binding is temporary and non covalent
ESC gets activated and catalyzed to its products
Enzyme lowers the activation energy

17. Enzymes – Principal of working cont
Enzymes – Principal of working cont. E controls the direction of reaction
Both, the enzyme and products are released upon completion of the reaction and enzyme is available for Reuse
The enzyme does not control the direction of the reaction.
It is controlled by the cell itself
Cell ↑the rate of forward and reverse reactions proportionally depending upon the body needs (Regulation)
www,wikibooks.org

18. Working of enzymes – the principals

19. Enzymes – Quantity and location Within and outside the cell
Most enzymes are produced in tiny quantities and catalyze reactions that take place within the cells like .
DNA/ RNA Polymerase and HMG CoA Synthase/Catalase
Digestive enzymes, however, are produced in relatively large quantities and act outside the cells/ lumen of the GIT
They cleave the dietary macromolecules like TG,Glycogen and Nucleic acids into smaller ones/ monomers

20. Allosteric or Additional sites Allosteric enzymes
Enzymes can also have sites other than active site that bind cofactors, which are needed for catalysis.
These are Allosteric sites and enzymes are Allosteric ones
These are the sites for binding of cofactors/products /substrates of catalytic reaction
Serve to regulate the enzyme activity via negative feed back

21. Allosteric enzymes

22. Denaturation of enzymes – heat and pH
Most enzymes can be denatured - unfolded and inactivated
by heating or chemical denaturants / change of pH
It disrupts the 3 structure of the protein (E) and
Results in loss of function
Denaturation of E may be reversible or irreversible depending upon the cause and damage to the enzyme

23. E. Denaturation – high temperature

24. E denaturation- change of pH Reversible Denaturation

25. Isoenzymes/ Isozymes – the Definition difference in sequence of AAs
Isoenzymes are generally the Multiple forms of the enzymes that differ in AA sequence but catalyze the :
Same chemical reaction.
These include the Isoenzymes of the :
Lactic Dehyrogenase (LDH) ,Creatine Kinase (CK) and Alkaline Phosphatase
online.org

26. Isoenzymes - Background
Isoenzymes display different electrophoretic mobility, regulatory and immunological properties
Isozymes are the result of gene duplication
These genes express the polypeptides chains that produce different subunits of the Isoenzymes
Like CK has 2 genes (M+B) that express 2 Polypeptide subunits – M and B
These produce CK1,CK2 and CK3

27. Isoenzymes – Basis for elevated levels
Different organs of the body contain the characteristic proportions of the different Isoenzymes
The pattern /conc. of Isozymes in the plasma may identify the site of tissue damage like CK has 3 forms
These Isoenzymes is present in 3 different tissues
The damage to these tissues releases  amount of respective CK Isoenzymes in circulation (Heart, brain and muscles)

28. Isoenzymes of Creatine Kinase

29. Isoenzymes of LDH

30. Creatine Kinase – Clinical importance
Level of Creatine Kinase CK (CKMB) is commonly determined for the diagnosis of Myocardial infarction – MI
These Isoenzymes are particularly useful when ECG is difficult to interpret especially when there have been :
Previous episodes of MI
Same is true for Cardiac Troponin T and I