Enzyme nomenclature, common and systemic name of enzymes
Classification and nomenclature of enzymes
Common names of enzyme
↪️Many enzyme have common names/trival names.
↪️Sometimes, the suffix-ase was added to the substrate for naming the enzymes
Example :
📍Urease for urea hydrolyzing enzyme
📍Lipase acts on lipids
📍nuclease on nucleic acids
📍lactase on lactose.
↪️In the early days, the enzymes were given names by their discoverers in anarbitrary manner.
For example :
The names pepsin, trypsin and chymotrypsin convey no information about the function of the enzyme or the nature of the substrate on which they act.
↪️These are known as trivial names of the enzymes which, however, fail to give complete information of enzyme reaction (type of reaction, cofactor requirement, etc).
⚠️Note : There are various point difference in enzyme classification and nomenclature. Enzymes given name according to their various points given below. Lastly we give information about Enzyme nomenclature by enzyme commission of I.U.B. So don't confuse about the points given in article. Just understand the concept.
Nomenclature and classification based on :
1. Substrate acted upon by the enzyme
2. Type of reaction catalyzed
3. Substrate acted upon and type of reaction catalyzed
4. Substance that is synthesized
5. Chemical composition of the enzyme
6. Substance hydrolyzed and the group involved
7. Overall chemical reaction taken into consideration
Don't make confusion about the word " nomenclature and classification ". Because enzyme named according to above points. So above are the basis of nomenclature. In point 7 Enzyme commission classified enzymes into six class and given proper nomenclature. i.e nomenclature is based on in which class the enzyme we put.
1. Substrate acted upon by the enzyme
The substance upon which an enzyme acts is called the substrate. In 1883, Duclaux named the enzymes by adding the suffix -ase in the name of the substrate catalyzed.
For example :
Enzymes acting on,
📍carbohydrates named as carbohydrases
📍proteins as proteinases
📍lipids as lipases,
📍Nucleic acids as nucleases
In simple
-ase + substrate ( Carbohydrate) = enzyme name ( carbohydrases )
This point is explained above as in common name.
2. Type of reaction catalyzed
The enzymes are highly specific as to the reaction they catalyze.
Formula :
-ase + reaction name ( hydrolysis ) = hydrolases
Similarly for,
📍Isomerases For isomerization
📍Oxidases For oxidation reaction
📍dehydrogenases for dehydrogenation reaction
📍Transaminases for transamination reaction
📍Transaldolases for transaldolation reaction
📍Transketolases for transketolation reaction
📍phosphorylases for phosphorylation reaction etc.
3. Substrate acted upon and type of reaction catalyzed
In this case two factors are considered here, means we can get clue of both i.e On which substrate enzyme will act and which action will be taken on that substrate.
Example :
📍Succinic dehydrogenase catalyzes the dehydrogenation of the substrate succinic acid.
📍L-glutamic dehydrogenase catalyzes a dehydrogenation reaction involving L-glutamic acid.
4. Substance that is synthesized
Formula :
-ase + substance synthesized
Example :
 |
| Image : Biotechnology A problem approach pp.144 |
Fumarase that forms fumarate irreversibly from L-malate.
i.e malate ⇆ fumarate
Enzyme = fumarase
5. Chemical composition of the enzyme
On the basis of chemical composition, the enzymes have been classified into three categories :
↪️Enzyme molecule consisting of protein only
Example :
📍pepsin, trypsin, urease, papain, amylase etc.
↪️Enzyme molecule containing a protein and a cation
Example :
📍carbonic anhydrase (containing Zn2+ as cation).
↪️Enzyme molecule containing a protein and a prosthetic group ( nonprotein organic compound )
Example :
📍Flavoprotein enzymes— glycine oxidase, pyruvate oxidase, histamine.
6. Substance hydrolyzed and the group involved
Carbohydrate-hydrolyzing enzymes
Glycosidase :
cellulase, amylase, sucrase, lactase, maltase
Lipid-hyrolyzing enzymes
lipases, esterases, lecithinases
7. Overall chemical reaction taken into consideration
⚠️Note : now all factors and basis were considered in this point
The International Union of Biochemistry (IUB) [ Now IUB change to International Union Of Biochemistry And Molecular Biology IUBMB ] appointed an Enzyme Commission in 1961.
This committee made a thorough study of the existing enzymes and devised some basic principles for the classification and nomenclature of enzymes. Since 1964, the IUB system of enzyme classification has been in force.
Classification Of Enzymes Into 6 classes
The Enzyme Commission (EC) has developed a rule for naming enzymes.
According to this rule, each enzyme is classified and named according to the type of chemical reaction it catalyzes.
Six classes of reactions are recognized
According to this system, the Enzyme Commission has given each enzyme a number with four parts.
Example :
EC 2.7.1.2 (EC number for enzyme hexokinase).
EC - Enzyme commission
2 - major class ( a transferase)
7 - subclass ( transfer of phosphate)
1 - sub-subclass ( an alcohol group as phosphate acceptor )
2 - The final digit denotes the enzyme, hexokinase or ATP: D-hexose-6 phosphotransferase.
Six Classes
EC 1 Oxidoreductase
EC 2 Transferases
EC 3 Hydrolases
EC 4 Lysases
EC 5 Isomerases
EC 6 Ligases
EC 1 Oxidoreductase
This class contains the enzymes catalyzing oxidation reaction. Oxidation of one group must be accompanied by the reduction of another.
Ared + Box → Aox + Bred
Examples
Dehydrogenases
Oxidases
Peroxidases
Hydroxylases
Oxygenases etc.
They catalyze electron transfer reactions.
In this class are included the enzymes catalyzing oxidoreductions of
CH—OH
C=O
CH—CH
CH—NH2
CH=NH groups.
EC 2 Transferases
This class catalyzes the reactions that involve the transfer of groups from one molecule to another. Example of such group include amino, carboxyl, carbonyl, methyl, phosphoryl and acyl ( RC=O ).
A-B + C → A + B-C
Example :
Transcarboxylase - carboxylate group transfer
Transaminase - amino group transfer from amino acid to keto acid
Kinases - Phosphate group transfer
EC 3 Hydrolases
Cleavage of bonds by adding water
A-B + H2O → A-H + B-OH
Example :
Phosphodiaesterase ( cleave phoaphodiester bond )
Phosphatases ( Remove phosphate from substrate )
Peptidase ( cleave amide bonds )
EC 4 Lyases (= Desmolases)
These are those enzymes which catalyze the removal of groups from Substrates by mechanisms other than hydrolysis or oxidation leaving double bonds or a new ring or conversely adding groups to double bonds
Lyases are enzymes that catalyzes the breaking of C-C, C-O, C-N, C-S.
A = B + HX → A-X + B-H
Example
Aldolases ( Removal of aldehydes via elimination reactions)
Synthases ( Link two molecules without involvement of ATP)
Dehydratases ( Removal of H20 via elimination reactions)
Decarboxylases ( Removal of CO, via elimination reactions )
EC 5 Isomerases
Isomerases catalyze several types of intramolecular rearrangements and yield isomeric forms.
A-B → B-A
Example :
Mutases
Cis-trans Isomerase
Epimerase
Racemases
EC 6 Ligases
Ligases catalyze the formation of C-C, C-S, C-O, and C-N bonds with simultaneous hydrolysis of ATP.
Other common names for ligases include synthetases, because they are used to synthesize new molecules.
A + B + ATP → A - B + ADP
Example :
Carboxylases
Seventh new class describes the important group of enzymes that catalyzes the movement of ions or molecules across membranes called as EC 7 translocases
References
Kumar Pranav, Praveen Verma and Usha Mina Biotechnology A Problem Approach . 5th ed., Pathfinder publication, 2019, pp. 99-101.
J. L Jain , Sunjay Jain and Nitin Jain Fundamentals Of Biochemistry . 6th ed., S. CHAND & COMPANY LTD. New delhi, 2005, pp. 333-344.
Author Shubham Tupe
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