For MD., MBBS, BDS, nursing students

1. ENZYMES
Prof. Dr. V.P. Ach

2. INTRODUCTION AND CLASSIFICATION

3. What shall we learn?
• Why should we learn about enzymes?
• Why medicos should know about them?
• Who thought about them first?- History
• How do we define them?
• How do we name them?- The
classification

4. Why enzymes???
 Two Fundamental Conditions for Life :
(1) able to self-replicate
(2) able to catalyze chemical reaction
efficiently and selectively
Example : a bag of sugar can be stored for
years, but it releases its chemical energy in
seconds in human body …… “ catalysis”
 Life depends on well-orchestrated series
of chemical reactions : E. coli has 4288
proteins, 2656 of which are characterized,
and 64% (1701) of the characterized ones
code enzymes

5. Chemical reactions are far slow to
maintain life
 Living system has designed catalysts
to fasten the specific reactions
Breakdown of nutrients to supply
energy
Assembly of building blocks
Diagnostic importance- diagnosis &
prognosis

6. Most of the history of Biochemistry is
enzyme research
• 1700- Meat digestion by stomach
• 1800- Conversion of starch to glucose by saliva
• 1850 Louis Pasteur .. Fermentation ( sugar →
alcohol)- said ferments are inseparable- Theory of
‘Vitalism’
• 1897 Edward Buchner …… yeast extract → enzyme
‘zymase’ (Sucrose → Alcohol)
• Willey Kunhe.. Coined ‘Enzyme’
• 1926 James Sumner … Urease crystallization →
protein- theory of vitalism rejected
• J.B.S. Haldane …… enzyme-substrate interaction

10. Milestones in enzyme study
• Koshland (1958)- “Induced fit” model was
proposed,
• Monod (1965)- “Allosteric model” of enzyme was
proposed,
• 1969- the first chemical synthesis of an enzyme
was reported, proving an enzyme is a protein
• Mechanisms of thousands enzymes have been
studied by X-ray crystallography and NMR
• DNA recombinant methods were used to
overproduce enzymes and to pinpoint the
important amino acids
• 2004, the first computer designed enzyme was
reported

11. What are Enzymes?
Enzyme Greek for “in yeast”

12. Definition
Enzymes are “Biocatalysts”, synthesized by living
cells and highly specific in their action.
They are:
Mostly proteins (Exception- Ribozymes)
Heat labile
Soluble in water
Colloidal
Precipitated by precipitation reaction
Contain 16% weight as nitrogen

13. Classification & Nomenclature
A. Recommended name
B. Systematic name
IUBMB
Unambiguous & Informative
But Cumbersome
6 major classes
Class.Subclass.sub-subclass.substrate

15. OTHLIL
Oxidoreductases→ Transfer of H, O or e-
Transferases → Transfer of gr other than H
Hydrolases → Cleave bond & add H2O
Lyases → Cleave bond without adding H2O
Isomerases → Intramolecular transfers
Ligases → ATP dependent condensation of
2 molecules

16. 1. Oxidoreductases
AH2 + B →A + BH2
Alcohol+ NAD+ ADH Aldehyde + NADH +H+
• Dehydrogenases (hydride transfer)
• Oxidases (electron transfer to molecular
oxygen)
• Oxygenases (oxygen transfer from molecular
oxygen)
• Peroxidases (electron transfer to peroxide).

17. 2. Transferases
A-R + B → A + B-R
• transfer of an atom or group of atoms (e.g.
acyl-, alkyl- and glycosyl- ), between two
molecules, but excluding such transfers as
are classified in the other groups (e.g.
Oxidoreductases and Hydrolases).
• Ex- Aminotransferases, all kinases,
transmethylases
• Hexose + ATP Hexokinase Hexose-6-P +
ADP

18. 3. Hydrolases
Cleavage of ester, ether, peptide or
glycosidic bond by addition of H2O
Ach + H2O acetylcholine esterase Choline + Acetate
Ex: All digestive enzymes, lipase, pepsin,
Trypsin, ALP, Urease

19. 4. Lyases
Cleave bond without addition of H2O
Fructose-1,6-BP Aldolase Glyceraldehyde-3-P
+ Dihydroxyacetone P
Ex: Fumarase, Histidase, HMG CoA lyase

20. 5. Isomerases
Can produce optical, geometrical or
positional isomers of substrates
Gly-3-P Triose P isomerase DHAP
Ex: Racemase, Epimerase

21. 6. Ligases (synthetases)
ATP dependent condensation of two
molecules
Acetyl CoA + CO2 + ATP Acetyl CoA Carboxylase
Malonyl CoA + ADP + Pi
Synthases and synthetases are different !!!
Ex: Glycogen synthase, ALA synthase

22. We are what we repeatedly do;
Excellence is then not an act but a

23. For more Medical Biochemistry ppt please
visit www.vpacharya.com