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

NOMENCLATURE &CLASSIFICATION OF ENZYMES

UG-05Semester-3rd

• 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)

ENZYMES

Trival name

• Gives no idea of source, function or reaction catalyzed by the enzyme.

• Example: trypsin, thrombin, pepsin.

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

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.

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

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

Classification of Enzymes4. 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

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 acidOxidase

Ascorbic acid + O2 Dehydro ascorbic acid

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

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+

CLASSIFICATION OF ENZYMESOxygenases:

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.

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

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

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

3. HYDROLASES Catalysing hydrolytic breakdown of different bonds. Most of the GIT

enzymes belong to this class

Enzymes hydrolyzing carbohydrates1. 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

3. HYDROLASES

Phospholipids Phospholipase lysophospholipids

Lecithin LysolecithinEnzymes Acting on Peptide Bonds:

exopeptidases carboxypeptidase amino acids

endopeptidase aminopeptidases e. g pepsin (smaller peptides)

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

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)

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

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 + CO2 + ATP Pyruvate Oxaloacetate + ADP + Pi

Carboxylase

Fatty acid + CoA + ATP Acyl CoA Acyl CoA (Activated fatty acid) + AMP + PiPi

Synthetase

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