Introduction properties, Nomenclature and Classification of Enzymes


GOALS : know the basics of the official nomenclature and functional.

know the 6 classes d’enzyme and their Functional characteristic.

S’practice writing the catalyzed reaction when’on

Knows the functional name of’an enzyme from

d’a given reaction following the indications



The aim of the course is to give a view of’set of metabolic enzymes.

All metabolic reactions are catalyzed by enzymes.

Enzymes are proteins that catalyze biological. They accelerate the metabolic reactions of’a living organism.

There is’has at least one different enzyme per catalyzed reaction, which represents thousands of’enzymes by organism. (3000 enzymes) Enzymes are spread over different cellular organelles and may, so, be qualified as « marker enzymes ».

Enzymes necessarily require to operate an annex molecule or cofactor, called Coenzyme.

These cofactors are small molecules (sometimes simple metal ion) linked to the enzyme protein.

Enzymes are biological catalysts of biochemical reactions :

* catalysts :

° They increase the reaction rates, without modifying the constant d’balanced, decreasing l’free energy d’activation ;

° They are found intact at the end of the reaction, although’they are intimately linked to the substrate and produced. (regenerated)

° operate at very low concentrations.

1is example :

Carbonic anhydrase is an enzyme present in all our cells.

It catalyzes the addition reaction of one molecule of water of a carbon dioxide molecule to form carbonic acid which dissociates at physiological pH in a bicarbonate ion and a proton.

This reaction is reversible and leads to a state of equilibrium that enzyme catalysis does not change.

2th example : approximately 30g of pure pepsin can digest almost two tonnes of white eggs in some hours.

* biological :

° are produced by the cell : all enzymes are
high molecular weight proteins, thermolabiles

metabolic (excp : ribozymes are RNAs endowed with’catalytic activity) ;

° They are specific :they transform a given substrate (substrate specificity) through a given reaction (specificity of’action) ;

° They are regulatable certain enzymes alter their catalytic activity in response to metabolic signals, which allows the’adjustment of the’metabolic supply on cellular demand.

Any enzyme is functionally recognized by a specific area called "active site" defined as the area or fixed(nt) the (s) substrates and coenzymes and where the reaction takes place. The active site plays a dual role : the substrate binding site and the catalytic site of.

The active site is located at the bottom of’a pocket of the inner area of ​​the protein.


A / Functional Classification : takes into account the name of the substrate of the’enzyme and the type of reaction catalyzed.

EXP : Pyruvate carboxylase.

=o Pyruvate PC =o oxaloacétate

When’enzyme uses 2 substrates is the means both indicating :

  • the radical donor substrate
  • The acceptor substrate of the radical,released
  • Type reaction catalyzed more "ase"

EXP : Glutamate pyruvate aminotransférase.

B / Names and official classification :

IU biochemistry codified the nomenclature and classification of enzymes called an official nomenclature.

All enzymes are listed under a number with 4 numbers separated by dots and preceded by EC (ENZYME COMMISSION)

Is (EC X1.X2.X3.X4)

XI : can vary from 1 at 6 => type of reaction

1 : oxydoréductases enzymes catalyzing

reactions d’oxidation-reduction by transferring H ions+ and electrons.

They are associated with coenzymes d’redox (OVER.


Many of these enzymes are known as :





Hvdrogénases. or Déshvdrogénases.

2 : transferases enzyme whose function is to catalyze the

transfer d’a functional group (an example ethyl or phosphate) d’a molecule (called donor) to another (called acceptor). for example, an enzyme catalyzing the following reaction will transferase:

A-X + B —► A + B-X where A is the donor and B l’acceptor.

3 : hydrolase form a class of enzymes that catalyze

reactions of’hydrolysis of’esters (esterases : carboxylester-hydrolases; peptide(peptidases :a-aminopeptido-aminoacidohydrolases, peptido-peptide hydrolases = endopeptidases), and glycosidic bonds (osidases : glucosidases).These enzymes do not require

usually coenzymes. They are activated by cations.

4 : lyase enzyme that catalyzes the breaking of different chemical bonds by means other than’hydrolysis or l’oxidation, forming and often a new double bond or a new cycle. For example a lyase enzyme catalyzes the transformation reaction of l’adenosine triphosphate (ATP) cyclic adenosine monophosphate (AMPc) : ATP => AMPc + PPi

5 : isomerase is an enzyme that catalyzes changes

within’a molecule, often by rearrangement of functional groups and conversion of the molecule into l’one of its isomers. Isomerases catalyze the type reactions :

A => B where B is an isomer A

EXP : Phosphoglucomutase is an enzyme of glycogenesis which catalyzes the reaction :

glucose-6-phosphate => glucose-1-phosphate, Like all mutase, its action consists only’to move a phosphate group between two carbons d’the same molecule.

6 : ligases : ligase is a enzyme which catalyzes

joining of two molecules by new covalent bonds with hydrolysis concomitant of’ATP or d’other identical molecules.

Many ligases are known as "synthase"

2X2 : sign l’belonging to a subclass. So, in Class I, the subclass indicates the nature of the donor’electron, in the classroom 2, class sub indicates the nature of the transferred group. In the classroom 3, the class under indicates the nature of the hydrolyzed bond. In the classroom 4, class sub indicates the nature of the cut connection. In the classroom 5, the subclass indicates the type of’isomerization. In the classroom 6, sub class indicates the nature of the link established.

X3 : sign l’belonging to a sub-subclass.

EXP in class I and in class I, sub- subclass indicates the nature of the’acceptor d’electron.

X4 : serial number in the group and the subgroup.

This official classification precise and complete the functional classification.

EXP :1a dehydrogenase glucose 6-phosphate catalyzes the reaction of glucose 6 phosphate -> 6-phosphogluconate,

Reaction of the pentose phosphate pathway, is’enzyme

EC : oxidoreductase (classel) whose donor’electrons is the group — C — OH (under classel) and l’acceptor d’electron is the subclass NADf), number d’order 49.

In Clinical Biochemistry, the enzymes can be used as a "parameter", in two separate orientations Semiological:

• seeking genetic enzyme deficiency

EXP : G6PD deficiency causes’hemolytic anemia.

• diagnosis of’organ, by measuring certain activities usually enzymatic


EXP : creatine kinase is a marker of cardiac cytolysis in the’myocardial infarction.