2. Enzymes
Biological catalysts, which speed up the reaction without being consumed.
Without enzymes, many of these reactions would not take place at a perceptible rate.
Enzymes accelerate almost all biochemical process, replication, repair, growth,
digestion etc.
4. Enzymes Vs. Catalysts
1- Enzymes have extraordinary catalytic power, often far greater than that of
synthetic or inorganic catalysts.
5. 2- They have a high degree of specificity for their substrates
3- Function in aqueous solutions
4- Require very mild conditions of temperature and pH.
8. 2- In some diseases, especially inheritable genetic disorders, there may
be a deficiency or even a total absence of one or more enzymes.
9.
10.
11. 3- Other disease conditions may be caused by excessive activity of an
enzyme.
12. 4- Measurements of the activities of enzymes in blood plasma,
erythrocytes, or tissue samples are important in diagnosing certain
illnesses.
13. 5- Many drugs act through interactions with enzymes.
14. 6- Enzymes are important in industries, food, textile, agriculture etc.
Pectinases
15. In the 1850s, Louis Pasteur concluded that fermentation of sugar into
alcohol by yeast is catalyzed by “ferments.”
He postulated that these ferments were inseparable from the structure of
living yeast cells; this view, called vitalism, prevailed for decades.
Enzymes: History
16. In 1897 Eduard Buchner discovered that yeast extracts could ferment
sugar to alcohol, proving that fermentation was promoted by molecules
that continued to function when even removed from cells.
17.
18. Frederick W. Kühne later gave the name enzymes (from the Greek
enzymos, “leavened”) to the molecules detected by Buchner.
The isolation and crystallization of urease by James Sumner in 1926
was a breakthrough in early enzyme studies.
Sumner found that urease crystals consisted entirely of protein, and he
postulated that all enzymes are proteins.
19. With the exception of a small group of catalytic RNA molecules all
enzymes are proteins.
The catalytic activity of a protein depends on the integrity of its native
conformation.
If an enzyme is denatured or dissociated into its subunits, catalytic
activity is usually lost.
Most Enzymes are proteins
20. Thus the primary, secondary, tertiary, and quaternary structures of
protein enzymes are essential to their catalytic activity.
21. One part of an enzyme, the active site, is particularly important.
Active site is divided into two sites
There are some amino acid residues that form temporary bonds with the
substrate (binding site) and residues that catalyse a reaction of that substrate
(catalytic site)
Active site of enzyme
22. The shape and the chemical environment inside the active site permits
a chemical reaction to proceed more easily.
23. The protein portion of an enzyme is
called “apoenzyme”.
Some enzymes require an additional
non-protein part to perform their
activities. The non-protein parts are
called cofactor (metal ions).
Non-protein partners of enzymes
24. If the non protein part is a complex organic or metallo-organic molecule
it is called as coenzyme.
A coenzyme or metal ion that is very tightly or even covalently bound to
the enzyme protein is called a prosthetic group.
A complete, catalytically active enzyme together with its bound
coenzyme and/or metal ions is called a holoenzyme.
25.
26.
27. Many enzymes have been named by adding the suffix “-ase” to the name of
their substrate or to a word or phrase describing their activity.
Other enzymes were named by their discoverers for a broad function,
before the specific reaction catalyzed was known.
This sort of classification was quite ambiguous as the same enzyme has two
or more names, or two different enzymes have the same name
Enzymes Classifications
28. International Union of Biochemistry and Molecular Biology
classified enzymes into six classes
29. .
1) Oxidoreductases: This is a very broad class of enzymes that catalyze the
many oxidation-reduction reactions found in biochemical pathways.
Oxidoreductases catalyze reactions in which at least one substrate gains
electrons, becoming reduced, and another loses electrons, becoming oxidized.
30.
31. 2) Transferases: This class of enzymes catalyze the transfer of a specific
functional group between molecules. Important subsets of transferases include
a) Kinases transfer phosphate groups, usually from ATP to another molecule
(such as hexokinase and glucokinase, that phosphorylate glucose and protein
kinases that phosphorylate protein hydroyxl groups),
b) Aminotransferases transfer amino groups that are important in amino acid
metabolism,
c) Acyltransferases transfer fatty acyl groups
d) Glycosyltransferases, which transfer carbohydrate residues.
35. 3) Hydrolases: Enzymes responsible to break the bond by using water
molecule.
Hydrolysis reactions refer to the cleavage of bonds by the addition of a
water molecule.
36.
37. 4) Lyases:
Lyases are the enzymes which cleave C-C, C-O, C-N or C-S bond
leaving a double bond or addition of groups to double bond.
Examples include aldolases (such as fructose diphosphate aldolase,
which is involved in glycolysis) and thiolases (such as b-ketoacyl-CoA
thiolase involved in the breakdown of fatty acids).
38.
39. 5) Isomerases: Transfer of groups within molecule to generate
isomeric forms.
For example, triose phosphate isomerase catalyzes the interconversion
between dihydroxyacetone phosphate and D-glyceraldehyde 3-
phosphate, which is essential for continuing glycolysis following
splitting of six carbon sugars into two three carbon sugars by fructose
diphosphate aldolase
40.
41.
42. 6) Ligases: Ligases are involved in synthesizing bonds between carbon
atoms and carbon, nitrogen, oxygen or sulfur atoms in reactions that are
coupled to the cleavage of the high energy phosphate of ATP or another
nucleotide.
Pyruvate carboxylase, a key enzyme in gluconeogenesis, is one
important ligase in metabolism.
43.
44. Each enzyme has specific EC number
The nomenclature was determined by the Enzyme Commission in 1961
(with the latest update having occurred in 1992), hence all enzymes are
assigned an “EC” number.
