Enzyme classification

Mr. Shardul S. Wagh shardulwagh@gmail.com

Introduction:

Enzymes are biocatalysts. They increase the rate of chemical reaction taking place within living cells without themselves suffering any overall change.

The name ‘enzyme’ (enG = in; zymeG = yeast) means ‘in yeast’

•Enzymes are protein in nature.

•They enhance the rate of reaction by lowering the activation energy.

•pH and temperature sensitive.

•Specific in nature.

Enzyme exploration was influenced by modern scientific approach of fermentation industry.

The name ‘enzyme ’ was coined by observing conversion of fruit juice (sugar) in to fine wine (alcohol) and release of Co2

How Enzymes work?????????

The reactants of enzyme –catalyzed reaction are termed substrates and each enzyme is quite specific in character, acting on a particular substrate to produce a particular product or products.

[E] + [S] [ES] [P] + [E]

Complexity of Biochemical Pathways

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How to remember and name these enzymes??????

Enzyme Nomenclature and Classification

With continuous increase in knowledge of enzymology, various systems have evolved to name and classify the enzymes.

1. Substrate acted upon by the enzyme.

2. Type of reaction catalyzed.

3. Substrate acted upon and type of reaction catalyzed.

4. Substrate that is synthesized.

5. Chemical composition of the enzyme.

6. Substance hydrolyzed and group involved.

7. I.U.B. classification.

1. Substrate acted upon by the enzyme.

The substance upon which an enzyme acts is called the substrate. Duclaux (1883) named the enzyme by adding the suffix – ase in the name of the substrate catalyzed.

Examples:

Carbohydrate – Carbohydrase

Protein – Proteinase

Lipid – Lipase

Maltose – Maltase

Sucrose – Sucrase

2. Type of Reaction catalyzed.

The enzymes are highly specific as to the reaction they catalyzed.

Hence this classification is based on adding suffix – ase in the name of reaction they catalyzed.

Hydrolase – hydrolysis.

Isomerases – isomerization.

Oxidase – oxidation.

Dehydrogenases – dehydrogenation.

Transaminases – transamination.

Examples:

3. Substrate acted upon and type of reaction catalyzed.

The name of some enzymes give clue of both the substrate utilized and the type of reaction catalyzed.

Eg.

Succinic dehydrogenase :- catalyzes dehydrogenation of substrate succinic acid.

L– glutamic dehydrogenase :- dehydrogenation of L –glutamic acid.

4. Substrate that is synthesized.

Few enzymes named by adding the suffix - ase to the name of the sustenance synthesized.

Eg.

Fumarase :- forms fumarate irreversibly by L – malate.

5. Chemical composition of the enzyme.

Classification based on chemical composition.

Examples:

Enzyme containing protein only :- Pepsin, Trypsin, Urease.

Enzyme containing protein & cation :- carbonic anhydrase.( Zn2+)

Enzyme containing protein & non protein:- (Prosthetic group)

Iron porphyrin enzyme:- Catalase, Cytochrome c peroxidase I & II

6. Substance hydrolyzed and group involved.

Examples:

Carbohydrate :- Cellulase, Amylase, Sucrase, - glucorinidase

Protein hydrolyzing enzymes :- Endopeptidases, exopeptidase.

Lipid:- Lipase, Esterase

7. I.U.B. Classification 1961

The chemical reaction catalyzed is specific property which distinguishes one enzyme from another.

I.U.B. used this criterion as a basis for classification and naming of enzymes.

The major features of this system are:-

Reactions are divided in to 6 major classes. Each with 4 to 13 subclasses.

1. Each enzyme has 2 parts – the first part is the name of substrate & second with suffix – ase, indicate type of reaction catalyzed.

2. Additional information regarding nature of reaction.

Eg. Malate dehydrogenase. (L- malate : NAD oxidoreductase.)

L- Malate +NAD+ Pyruvate +Co2 +NADH+H+

I.U.B. Classification contd…

4.Each enzyme has been allotted systemic code called Enzyme commission number (E.C.) it consist of series of 4 digits.

Example. Alcohol Dehydrogenase. (E.C.1.1.1.1.)

1.1.1.1.Class

Sub Class (acting on CH – OH group of electron donor)

Sub Sub Class (electron acceptor)

Enzyme Number

Class 1. Oxidoreductase (Oxidation n Reduction)

Class 2. Transferase (Transfer of Group)

Class 3. Hydrolase (Hydrolysis)

Class 4. Lyases (Lysis)

Class 5. Isomerases (Isomers)

Class 6. Ligases (To joint)

Class 1. Oxidoreductase (Oxidation n Reduction)

These enzymes catalyze the transfer of H atoms, O- atoms or electrons from one substrate to another.

Eg. 1.1.1.1. (Alcohol Dehydrogenase)

Acting on (CH – OH) alcohol group of electron donor.

Electron acceptor.

Enzyme serial Number.

Other example is Lactate Dehydrogenase (E.C. 1.1.1.27)

2. Transferase (Transfer of Group)

Catalyzes the reaction AX + B BX + A

While giving name to particular enzyme Enzyme commission recommends that the name of transferase should end “X – Transferase” where X – is the group transferred.

Eg. 2.1.1 methyltransferases ( - CH3) (transfer from first Carbon)

Eg. ATP : D- Hexose –6 – phosphatases (2.7.1.1) (Hexokinase)

D- hexose + ATP D – Hexose – 6 – (P) + ADP

Class 3. Hydrolase (Hydrolysis)

These types of enzymes catalyzes the reaction of hydrolysis of ester, glycosyl by addition of water molecule.

Enzymes catalyzes hydrolytic reaction.

A – X + H2O X – OH + HA

Eg. Orthophosphoric monoester phosphohydrolase (E.C. 3.1.3.1)

(Alkaline phosphatase)

Organic (P) inorganic (P)

Class 4. Lyases (Lysis)These enzymes catalyses the non hydrolytic removal of groups from substrates often leaving double bonds.

Eg. L – Histidine carboxy – lyase (E.C.4.1.1.22)

(Histidine – decarboxylase)

Histidine Histamine.

Class 5. Isomerases (Isomers)Enzymes catalyzing isomerization reaction

Eg. Alanine racemase (E.C. 5.1.1.1)

L- alanine D – alanine.

Class 6. Ligases (To joint)

Enzymes catalyzed the synthesis of new bonds coupled to the breakdown of ATP or other nucleoside triphosphates.

X + Y + ATP X – Y + ADP + Pi

E.C. 6.3.1. Acid - ammonia ligases.