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HISTORY OF ENZYMES

In 1877-“Enzyme”term was coined by Wilhelm Kuhne. The term Enzyme means “In Yeast”.

In 1897- Eduart Buchner found that sugar was fermented by yeast extracts even when there was no living yeast cells. He named the enzyme “zymase”

In 1926- James B. Sumner showed that enzyme urease was a pure protein.

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DIFFERENCE BETWEEN ENZYME AND CATALYSTS

Enzyme	Catalyst
Enzymes are proteins that increase rate of chemical reactions converting substrate into product	Catalysts are substances that increase or decrease the rate of a chemical reaction but remain unchanged.
Enzymes are high molecular weight globular proteins	Catalysts are low molecular weight compounds
The two types of enzymes are: Activating enzymes and Inhibitory enzymes	The two types of catalysts are positive and negative catalysts

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Classification & Nomenclature Of Enzymes, Specificity Of Enzyme Action (Lock & Key Model & Induced Fit Model)

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TRIVAL NAME�

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

Example: trypsin, thrombin, pepsin.

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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

Lactate dehydrogenase

Pyruvate + NADH + H+ Lactate + NAD+

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ENZYME CLASSIFICATION

The Enzyme Commission number (EC number) is a numerical classification scheme for enzymes, based on the chemical reactions they catalyze.

As a system of enzyme nomenclature, every EC number is associated with a recommended name for the respective enzyme.

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EC NUMBERS

EC numbers are four digits, for example a.b.c.d

“a” is the class
“b” is the subclass
“c” is the sub‐subclass
“d” is the sub‐sub‐subclass.

The “b” and “c” digits describe the reaction
“d” digit is used to distinguish between different enzymes of the same function based on the actual substrate in the reaction.

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Example: for Alcohol:NAD+oxidoreductase EC number is 1.1.1.1
Systemic name is Alcohol dehydrogenase

Alcohol dehydrogenase

Alcohol + NAD+ Aldehyde + NADH

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�The Six Classes

EC 1. Oxidoreductases
EC 2. Transferases
EC 3. Hydrolases
EC 4. Lyases
EC 5. Isomerases
EC 6. Ligases

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� EC 1. OXIDOREDUCTASES

It catalyzes the transfer of hydrogen or oxygen atoms or electrons from one substrate to another, also called oxidases, dehydrogenases, or reductases.

It catalyzes ‘redox’ reactions, an electron donor/acceptor is also required to complete the reaction
E.g. A^– + B → A + B^–

Glyceraldehyde-3-phosphate dehydrogenase enzyme

P_i + glyceraldehyde-3-phosphate + NAD⁺ → NADH + H⁺ + 1,3-bisphosphoglycerate

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��EC 2. TRANSFERASES�

It catalyze group transfer reactions, excluding oxidoreductases (which transfer hydrogen or oxygen and are EC 1).

A‐X + B ↔ BX + A
Example Aspartate aminotransferase

Aspartate aminotransferase

Aspartate + α-ketoglutarate Oxaloacetate + Glutamate

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EC 3. Hydrolases�

It catalyze hydrolytic reactions.
It includes lipases, esterases, nitrilases, peptidases/proteases.
A‐X + H2O ↔ X‐OH + HA
Acetylcholineesterase catalyses the following reaction

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EC 4. Lyases �

It catalyses non- hydrolytic splitting of bonds

Example Aconitase enzyme catalyses the reaction

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EC 5. Isomerases �

Isomerases are a general class of enzymes that convert a molecule from one isomer to another.
Isomerases facilitate intramolecular rearrangements in which bonds are broken and formed.
The general form of such a reaction is as follows: A–B → B–A.
Phosphoglucoisomerase enzyme catalyses the following reaction

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EC 6. Ligases�

Ligase enzymes catalyses joining of two molecules at the expense of high energy molecules ATP
Glutamine synthetase catalyses the following reaction