The chemical nature of enzymes, naming and classification of enzymes.ppt

The chemical nature of enzymes, naming and classification of enzymesThe chemical nature of enzymes, naming and classification of enzymes
naming of enzymes.cclassification of enzymes

1. The chemical nature of enzymes, The chemical nature of enzymes,
naming and classification of enzymesnaming and classification of enzymes
Prof.Zhao Yun TaoProf.Zhao Yun Tao
Present by Rashid khanPresent by Rashid khan
ID: 2252403139ID: 2252403139
Major: Food Science and EngineeringMajor: Food Science and Engineering
1

2. ENZYMESENZYMES
Definitions--Definitions--
 A biomolecule either Protein or RNA, that catalyze a
specific chemical reaction, enhance the rate of a
reaction by providing a reaction path with a lower
activation energy

3. Enzymes activity Enzymes activity

4. Fundamental PropertiesFundamental Properties
1) Catalytic power-speeding up reactions 10
8

to 10
20
fold.
They speed up reactions without being
used up.
2) Specificity
a) for substrate - ranges from absolute to
relative
b) for reaction catalyzed
3) Regulated-- some enzymes can sense
metabolic signals.

5. Catalytic PowerCatalytic Power
Catalytic Power is defined as the Ratio of the Enzyme-
Catalyzed Rate of a Reaction to the Uncatalyzed Rate
e.g. Urease-
At 20°C, the rate constant for the
enzyme-catalyzed reaction is 3 X
10
4
/sec
the rate constant for the uncatalyzed
hydrolysis of urea is 3 X 10
10
/sec
10
14
is the ratio of the catalyzed rate to
the uncatalyzed rate of reaction

7. Cont..
The substances upon which an enzyme acts are
traditionally called- substrates
The selective qualities of an enzyme are collectively
recognized- specificity
The specific site on the enzyme where substrate binds and
catalysis occurs is called- active site

8. Regulation

9. HistoryHistory
In 1833, diastase (a mixture of amylases) was the
first enzyme to be discovered, quickly followed by
other hydrolytic enzymes such as pepsin and
invertase, but the term enzyme was only coined in
1877 by Wilhelm Kühne.The concept of catalysts,
chemicals facilitating a reaction without
undergoing any change themselves, was
introduced in 1836 by Berzelius who quickly
hypothesized that enzymes were such catalysts.


10. Classification and Classification and
NomenclatureNomenclature
1. Often named by adding the suffix -ase to the name of
the substrate upon which they acted
e.g. Urease, DNA Polymerase

11. Cont..
2. Names bearing little resemblance to their activity
e.g. catalase - the peroxide-decomposing enzyme
Proteolytic enzymes (proteases) of the digestive tract
Trypsin- Gr. Word Tryein means to wear down
Pepsin- Pepsis means digestion

12. IUB nomemclatureIUB nomemclature
1956 - to create a systematic basis for enzyme nomenclature
4 digit numbered code
first digit - major class
Second digit - sub class
third digit - sub sub class
final digit - specific enzyme

13. 2.7.1.12.7.1.1
ATP: glucose phosphotransferaseATP: glucose phosphotransferase
2- class name (transferase)
7- subclass name (phosphotransferase)
1- sub sub class (hydroxyl group as acceptor)
1- specific enzyme (D- glucose as phosphoryl group
acceptor)

14. Enzyme classificationEnzyme classification
Six classes
1. Oxidoreductase- transfer of reducing equivalents from
one redox system to another
e.g. Alcohol Dehydrogenase
Lactate dehydrogenase
cytochrome oxidase

15. 2. Transferase2. Transferase
functional group is transferred from one compound to
another
e.g. kinases
transaminase
phosphorylase

16. 3. Hydrolase3. Hydrolase
cleave C-O, C-N, C-S or P-O etc bonds by adding water
across the bond
e.g.lipase
acid phosphatase
(important in digestive process)

17. 4. Lyases4. Lyases
cleave C-O, C-N, or C-S bonds but do so without addition of
water and without oxidizing or reducing the substrates
e.g.aldolase
fumarase
Carbonic anhydrase

18. 5. Isomerase5. Isomerase
catalyze intramolecular rearrangements of functional
groups that reversibly interconvert to optical or
geometric isomers
e.g.Triose isomerase
phosphohexose isomerase
mutase

19. 6. Ligase6. Ligase
catalyze biosynthetic reactions that form a covalent bond
between two substrates utilizing ATP-ADP
interconversion
e.g.glutamine synthetase
DNA- ligase

20. SpecificitySpecificity
highly specific compared to other catalyst
catalyzes only specific reaction
3 types
1.Stereospecificity/ optical specificity
2.Reaction specificity
3.Substrate specificity

21. Optical specificityOptical specificity
able to recognise optical isomers of the substrate
Act only on one isomer
e.g. enzymes of amino acid metabolism (D & L Amino acid
oxidase)
Isomerase do not exhibit stereospecificity

22. Reaction SpecificityReaction Specificity
catalyze only one specific reaction over substrate
e.g. amino acid can undergo deamination, transamination,
decarboxylation and each is catalysed by separate
enzyme

23. Substrate specificitySubstrate specificity
specific towards their substrates
e.g. glucokinase and galactokinase- both transfer phophoryl
group from ATP to different molecule
3 types
a.Absolute
b.Relative substrate
c.broad

24. Absolute substrate specificityAbsolute substrate specificity
Act only on one substrate
e.g. urease

25. Relative substrate specificityRelative substrate specificity
act on structurally related substrates
Further divide into
i.Group dependent- act on specific group e.g. trypsin-
break peptide bond between lysine and arginine,
Chymotripsin act on aromatic AA
ii.Bond specificity- act on specific bond e.g. proteolytic
enzyme, glycosidase

26. Broad specificityBroad specificity
Act on closely related substrates
e.g. hexokinase- act on many hexoses

27. Chemical Nature & Chemical Nature &
Properties of EnzymeProperties of Enzyme
Protein or RNA
Tertiary structure and specific conformation- essential
for catalytic power
Holoenzyme- functional unit
Apoenzyme & coenzyme

28. Prosthetic group Coenzyme/
cofactor
Non protein
molecule
Non protein
molecule
Tightly
(covalently) bound
Loosely bound
Stable
incorporation
Dissociable
Cannot be
dissociated
Seperable by
dialysis etc

29. ContCont..
Monomeric Enzyme- made of a single
polypeptide e.g. ribonuclease, trypsin
Oligomeric Enzyme- more than one
polypeptide e.g. LDH, aspartate
carbamoylase
Multienzyme complex- specific sites to
catalyse different reactions in sequence.
Only native conformation is active not
individual e.g. pyruvate dehydrogenase

30. Multienzyme Complexes and Multienzyme Complexes and
Multifunctional EnzymesMultifunctional Enzymes
In a number of metabolic pathways, several
enzymes which catalyze different stages of
the process have been found to be
associated non covalently giving a
multienzyme complex.
Examples: Pyruvate Dehydrogenase Complex ;
Electron Respiratory Chain
In other cases, different activities may be
found on a single multifunctional polypeptide
chain. The presence of multiple activities is
on a single polypeptide chain is usually the
result of a gene fusion event