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

2. ENZYMES
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 + CO2
Malate NAD oxidoreductase (Decarboxylating)

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

7. CLASSIFICATION OF ENZYMES
Formulated by the enzyme commission of I.U.B six major classes based on the type of reactions catalyzed
Oxidoreductases
Catalyzing oxidation reduction reactions
Transferases
Catalyzing group transfer
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 + O2 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
Is an enzyme that oxidizes a substrate by transferring the oxygen from molecular oxygen O2 (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 (O2) 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.
Oxygenases:

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)
Pyruvic acid Alanine

14. 2.TRANSFERASES
Transmethylases. Catalyzing transfer of methyl group between to substrates e.g. COMT
Catechol-O-
methyltransferase (COMT)
Noradrenalin Adrenaline
+ CH3
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
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 Enzymes hydrolyzing carbohydrates
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 exopeptidases carboxypeptidase amino acids
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. + H2O 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 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
Pyruvate + CO2 + ATP Pyruvate Oxaloacetate + ADP + Pi
Carboxylase
Fatty acid + CoA + ATP Acyl CoA Acyl CoA (Activated fatty acid) + AMP + PiPi

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 ", 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  are those hydrolases that cleave off the amino-terminal amino acid from a polypeptide
EC  are those that cleave off the amino-terminal end from a tripeptide