This document provides information about enzymes, including their properties, classification, and roles in biochemical processes and medicine. Some key points:
- Enzymes are proteins that catalyze chemical reactions in living cells without being consumed in the process. They work by lowering the activation energy of reactions.
- There are six major classes of enzymes based on the type of reaction catalyzed: oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases.
- Enzymes require cofactors like metal ions or organic coenzymes derived from vitamins to function. The active holoenzyme is made up of an apoenzyme and its cofactors.
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2. • Biocatalysts, thermoliable, proteins (except ribozyme) and highly
specific.
• Increases the rate of chemical reactions taking place within living cells
without participating in the reaction - Enzyme.
• Enzyme names usually ends in “-ase” (eg: aminotransferase, glucokinase,
carbonic anhydrase)
3. Biomedical Importance Of Enzymes
• Chemical reactions are catalyzed by enzymes
• Helps to understanding the cellular and physiological functions
• Necessary for digesting food (enzymes are secreted in inactive form
zymogens or proenzymes- like chymotrypsinogen - chymotrypsin)
• Abnormalities of enzymes produces diseases e.g. galactosemia,
phenylketonuria etc.
4. • Also helps in diagnosis and treatment of diseases
e.g. Increased serum amylase helps in diagnosis of pancreatitis,
Streptokinase – used as medicine to dissolve blood clot in MI
• Used to monitor the progress and outcome of diseases
e.g. liver enzymes SGOT, SGPT and alkaline phosphatase
• Used in research
e.g. Restriction endonuclease in recombinant DNA technology
5. • Enzyme characterized by a code number called EC number, consisting
of four digit
– First digit: main class that characterizes the type of reaction they catalyzed
– Second digit: sub class, indicates the type of group involved in this reaction
– Third digit: sub-sub class, donates the substrate on which enzyme acts
– Fourth digit: specifies the individual enzyme. Indicates the systematic serial
number and name
6. Example: lactate dehydrogenase EC (1.1.1.27)
– First digit: indicates that the enzyme is an oxido-reductase
– Second digit: indicates that the enzyme acts on the CH-OH group
which is the donor of hydrogen
– Third digit: indicates that the acceptor is NAD
– Fourth digit: is the serial number of the enzyme in EC group
7. CLASSIFICATION OF ENZYME
• Enzymes are divided into six major classes based on the types of reaction
catalyzed by IUB or IUBMB (International union of biochemistry & molecular
biology)
Class 1: Oxidoreductases
Class 2: Transferases
Class 3: Hydrolases
Class 4: Lyases
Class 5: Isomerases
Class 6: Ligases
8. Class 1: Oxidoreductases
• Catalyzes oxidation - reduction reactions and involved in transfer of
hydrogen from one substrate to another
E.g.: Alcohol dehydrogenase, lactate dehydrogenase, Reductases, Oxidases,
Peroxidases
Ethanol + NAD+ Acetaldehyde + NADH+H+
Alcohol dehydrogenase
Pyruvate+ NAD+ Lactate+ NADH+H+
Lactate dehydrogenase
9. Class 2: Transferases
• Transfers functional groups(amino, carboxyl, methyl or phosphoryl
etc.) from one substrate to another
E.g.: Kinases, Amino transferases, Transcarboxylase
Glucose + ATP Glucose-6-Phosphate + ADP
Glucokinase / Hexokinase:
Aspartate Aminotransferase (AST):
L- Aspartate + α- Ketoglutarate Oxaloacetate + L-Glutamate
Alanine amino transferase (ALT):
L- Alanine + α- Ketoglutarate Pyruvic Acid + L-Glutamate
PLP
PLP
A-X +B A + B-X
10. Class 3: Hydrolases
• Catalyzes the cleavage of a molecule (C-O, C-N. C-C etc.) by addition of
water, hydrolysis
E.g.: Digestive enzymes, pepsin, trypsin, Lactase, Maltase, Sucrase, Lipase ,
Acid phosphatase, Urease,
Lactose+H2O α-D Glucose + α-D-Galactose
Lactase
A – B +H2O A - OH + B-H
11. Class 4: Lyases
• Catalyzes the reactions by introducing double bond. eg: Aldolase
E.g. Fructose 1,6 BP-- Glyceraldehyde-3-P + DHAP
12. Class 5: Isomerases
• Catalyzes the intermolecular rearrangement in a molecule.
E.g.: epimerases, isomerases or mutases
Glucose-6-P Fructose-6-P
Glucose -6-P isomerase
ABC CAB
13. Class 6: Ligases or Synthetases
• Catalyzes the joining of two compounds or molecules coupled with the
hydrolysis of ATP
E.g.: Pyruvate carboxylase, Glutamine synthetase, Acetyl-CoA
carboxylase
Glutamate + NH4
+ + ATP Glutamine + H2O +ADP +Pi
Glutamine Synthetase:
A + B + ATP AB + ADP +Pi
15. • Enzymes: increases the rate of reaction by acting as catalysts
• Velocity (or) rate of the reaction: Change in amount (moles) of substrates or
products per unit of time per enzyme
• Substrate: molecule acted upon by the enzyme to form a product
• Product: molecule obtained from enzyme reaction
• Apo enzyme is made up of only protein molecules
16. Ions Enzymes
Cu2+ Cytochrome oxidase
Fe2+ or Fe3+ Catalase, Peroxidase
Mg2+ Hexokinase, glu-6-Phasphatase, Pyruvate kinase
Mn2+ Arginase, ribonucleotide reductase
Mo Nitrate reductase
Se+ Glutathione peroxidase
Ze2+ Carboni anhydrase, alcoholic dehydrogenase
Cofactors
Enzymes required an additional non protein chemical component for its optimum
activity
Maybe either one or more inorganic ions
17. Coenzyme
– Non protein part of enzyme maybe either organic or metalloorganic molecules
– Derivatives of B-complex Vitamins
Vitamin Co enzymes Functions
Thiamine (vit B1) Thiamine pyrophosphate (TPP) Oxidative decarboxylation
Riboflavin (vit B2) Flavin adenine dinucleotide (FAD)
& Flavin mononucleotide (FMN)
Oxidation –reduction reactions
Niacin (vit B3) Nicotinamide adenine dinucleotide
(NAD) & NADP
Oxidation –reduction reactions
Pantothenic acid (vit-B5) Coenzyme A (CoA) Acyl carrier
Pyridoxal (vit B6) Pyridoxal phosphate (PLP) Transamination, deamination,
decarboxylation
18. Role of coenzymes
• Loosely or tightly bound as prosthetic group
• Transfer of H+ ions or electrons in oxidation-reduction reactions
• Transfer of groups other than H+ like amino group, acetyl group, etc.
Aminotransferase / transaminase
19. Holoenzyme:
Apoprotein + Cofactor / coenzymes = Holoenzyme
• The protein part of holoenzyme is apoenzyme and Non-protein part of the
holoenzyme is cofactor and coenzyme.
20. Zymogens or Proenzymes
• Inactive precursor or enzyme, which must be cleaved to be activated.
• Prevents them from catalyzing reactions in the cell where they are
synthesized
• Chymotrypsin is secreted by the pancreas as Chymotrypsinogen
(Trypsin cleaves off a small peptide from N-terminal region of Chymotrypsinogen)
21. (Secreted by duodenal epithelial
cells)
Hydrolyzes small non
polar a.a’s like Ala, Ser
& Gly
Carboxyl group of
aromatic a.a’s &
Splits peptide
linkages of Leu,
Met, Asn & His
Removes the carboxyl
terminal a.a’s from
peptides
Enterokinase
22. Active Site
• Enzyme molecules contain a special pocket or cleft
called active site,
• It involved in the substrate binding and catalysis.
• Active site is made up of amino acids (commonly
found serine, Asp, His, Cys, Lys, Arg, Glu, Tyr etc)
• It is not rigid in structure and shape.
• It is rather flexible to promote the specific substrate
binding.
• The substrate binds at the active site by weak non
covalent bonds
23. • Michaelis and Menten have proposed a hypothesis for enzyme action
• Enzyme molecule (E) first combines with a substrate molecule (s) to form an enzyme
substrate (ES) complex, which further dissociates to form product (P) & enzyme (E)
back.
24. Multienzyme complexes
• These are stable assemblies of more than one enzyme, generally involved
in sequential catalytic transformations.
• These are distinct from a multienzyme polypeptide, in which multiple
catalytic domains are found in a single polypeptide chain.
• However only the intact multienzyme complex is functional and not the
individual units.
• Example for Multienzyme complexes
Pyruvate dehydrogenase (PDH) complex
Fatty-acyl-CoA Synthase complex
