enzymes-nomenclature and classification.ppt

enzymes-nomenclatureclassification.ppt

1. NOMENCLATURE &CLASSIFICATION
OF ENZYMES
UG-05
Semester-3rd

2. •Biological catalysts which speed up the rate of reaction
without becoming part of the reaction but themselves cannot
initiate any chemical reaction.
•Enzymes :
•First name is of substrate
•second, ending in “ASE” indicating type of reaction catalyzed.
•Clarify the reaction , e.g. Malic Enzyme
•L- Malate + NAD  Pyruvate + NADH-H + CO
2
•Malate NAD oxidoreductase (Decarboxylating)
ENZYMES

3. Trival name
•Gives no idea of source, function or reaction
catalyzed by the enzyme.
•Example: trypsin, thrombin, pepsin.

4. Systematic Name
•According to the International union Of
Biochemistry an enzyme name has two parts:
-First part is the name of the substrates for
the enzyme.
-Second part is the type of reaction catalyzed
by the enzyme.This part ends with the suffix
“ase”.
Example: Lactate dehydrogenase

5. EC number
•Enzymes are classified into six different groups
according to the reaction being catalyzed.
•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.
•The classification does not take into account amino
acid sequence (ie, homology), protein structure, or
chemical mechanism.

6. EC numbers
•EC numbers are four digits, for example a.b.c.d, where
“a” is the class, “b” is the subclass, “c” is the sub-
subclass, and “d” is the sub-sub-subclass. The “b” and
“c” digits describe the reaction, while the “d” digit is
used to distinguish between different enzymes of the
same function based on the actual substrate in the
reaction.
•Example: for Alcohol:NAD
+
oxidoreductase EC
number is 1.1.1.1

7. CLASSIFICATION OF ENZYMES
Formulated by the enzyme commission of I.U.B six major
classes based on the type of reactions catalyzed
1.Oxidoreductases
•Catalyzing oxidation reduction reactions
2.Transferases
•Catalyzing group transfer
3.Hydrolases
•Catalyzing hydrolytic breakdown

8. Classification of Enzymes
4.Lyases
•Catalysing removal of groups by mechanism other than
hydrolysis and leaving behind double bonds
5.Isomerases
•Catalysing interconversion of isomers
6.Ligases
•Catalysing formation of bonds and new compounds
1. Oxidoreductases
–Catalysing oxidation reduction reaction where one
substrate is oxidized and other is reduced

9. CLASSIFICATION OF ENZYMES
Oxidases. Catalyzing oxidation of the substrate and
atomic oxygen acts as recipient of hydrogen e.g.
Ascorbic acid oxidase, Cytochrome oxidase, Tyrosinase

Ascorbic acid
Oxidase
Ascorbic acid + O
2
Dehydro ascorbic
acid

10. CLASSIFICATION OF ENZYMES
Aerobic Dehydrogenases.
Catalyzing oxidation of the substrate and molecular
oxygen acts as recipients of hydrogen e.g. Glucose
oxidase, L amino acid dehydrogenase, Xanthene
dehydrogenase

glucose oxidase
Glucose Gluconolactone

11. CLASSIFICATION OF ENZYMES
Anaerobic Dehydrogenases. Catalyzing oxidation of
the substrate and coenzymes act as recipients of hydrogen
e.g. Lactate Dehydrogenase with NAD and Glucose 6
phosphate dehydrogenase with NADP
Lactate
dehydrogenase
Lactic acid Pyruvic acid
+ NAD + NADH – H
+

12. CLASSIFICATION OF ENZYMES
Oxygenases:
Is an
 enzyme that oxidizes a substrate by transferring
the
 oxygen from molecular oxygen O
2
 
(as in air) to it.
Types :
a. Monooxygenases:
Transfer one oxygen atom to the substrate, and reduce the
other oxygen atom to
 water.
b. Dioxygenases:
Incorporate both atoms of molecular oxygen (O
2
) into the
product(s) of the reaction.
Among the most important monooxygenases are
the
 cytochrome P450 oxidases, responsible for breaking
down numerous chemicals in the body.

13. 2.TRANSFERASES
Transaminases. Catalyzing transfer of amino group between
an amino acid and a ketoacid e.g. Aspartate transaminase (AST),
Alanine transaminase (ALT)
Aspartate
transaminase (AST)
Glutamic acid +  ketoglutaric
acid +
Oxalo acetic acid Aspartic acid
Alanine
transaminase (ALT)
Glutamic acid +  ketoglutaric
acid +
Pyruvic acid Alanine

14. 2.TRANSFERASES
Transmethylases. Catalyzing transfer of methyl group between
to substrates e.g. COMT
Catechol-O-
methyltransferase (COMT)
Noradrenalin Adrenaline
+ CH
3
Transpeptidases. Catalyzing transfer of amino acids to
substrates e.g. Benzyl-SCoA transpeptidase
Benzyl-SCoA transpeptidase
Benzyl - SCoA Hippuric acid
+ Glycine

15. 2. TRANSFERASES
Phosphotransferases. Catalyzing transfer of phosphate
group to substrates e.g. Hexokinase, glucokinase
2.7.1.1 ATP D hexose 6 phosphotransferase [Hexokinase]
ATP + Glucose Hexokinase ADP + D-Glucose –6-P
Acetyltransferase. Catalyzing transfer of acetyl group to
substrates e.g. choline acetyltransferase
Acetyl-CoA+ Choline  CoA + Acetyl- Choline

16. 3. HYDROLASES
Catalysing hydrolytic breakdown of different bonds. Most of the GIT
enzymes belong to this class
Enzymes hydrolyzing carbohydrates
1. Polysaccharidases
Starch Amylase Maltose, maltotrios, dextrins
2. Oligosaccharidases
Dextrins Dextrinase glucose
3. Disacharidases
Maltose, Lactose, Sucrose Disacharidases Maltase, Lactase, Sucrase
monosaccharides
Enzymes Hydrolyzing Lipids
Triacyl glycerol lipase monoacyl glycerol + 2 F.F.A

Cholesterol ester cholesterol free cholesterol + FFA
esterase

17. 3. HYDROLASES
Phospholipids Phospholipase lysophospholipids
Lecithin Lysolecithin
Enzymes Acting on Peptide Bonds:

exopeptidases carboxypeptidase amino acids

endopeptidase aminopeptidases e. g pepsin (smaller peptides)

18. 3. HYDROLASES
Tripeptidase : Tripeptide  A.A
Dipeptidase : Dipeptide  A.A
Phosphatases
1.Phosphomonoesterases:
Glucose – 6.P. + H
2O Phosphatase G 6. Phosphate Glucose +Pi
2.Phosphodiesterases:
Removal of phosphate Group of diesters breakdown of 3’-5’ p
linkages in cyclic AMP

19. 4. LYASES
•Catalysing reactions in which groups are removed without
hydrolysis leaving a double bond or add groups to already existing
double bonds.
CH3. CO. COOH CH3. CHO+ CO2
(pyruvate) pyruvate decarboxylase (acetaldehyde)
COOH.CH = CH. COOH Fumerase COOH-CHOH. CH2-COOH
(Fumaric acid) (malic acid)

20. 5. ISOMERASES
•Involved in inter conversion of pair of isomeric compounds
•Glucose 6. P Phosphogluco mutase glucose I.P
•Glucose 6.P Phosphohexose isomerase Fructose 6.P
• All trans retinene Retinene 11- CIS retinene
Isomerase

21. 6. LIGASES
•Catalyze reactions in which linking together of two
molecules occur coupled with the breakdown of a high
energy phosphate bonds like ATP, GTP
Acetate + CoA +ATP Acetyl CoA Acetyl CoA+AMP
Synthetase
Succinate + CoA + ATP Succinyl CoA Succinyl CoA + ADP+ Pi
Synthetase
Pyruvate + CO
2
+ ATP Pyruvate Oxaloacetate + ADP + Pi
Carboxylase
Fatty acid + CoA + ATP Acyl CoA Acyl CoA (Activated fatty acid) + AMP + PiPi
Synthetase

22. EC
•Every enzyme code consists of the letters "EC" followed by four
numbers separated by periods. Those numbers represent a
progressively finer classification of the enzyme.
•For example, the
 
tripeptide aminopeptidases 
have the code "EC
3.4.11.4", whose components indicate the following groups of
enzymes:
•EC 3 
enzymes are hydrolases (enzymes that use water to break up
some other molecule)
•EC 3.4 
are hydrolases that act on peptide bonds
•EC 3.4.11 
are those hydrolases that cleave off the amino-
terminal
 amino acid from a polypeptide
•EC 3.4.11.4 
are those that cleave off the amino-terminal end from
a
 tripeptide