Enzyme Nomenclature
Systematic and Descriptive Naming
Enzymes are named systematically to reflect the type of reaction they catalyze.
Typically, the suffix "-ase" is added to the name of the substrate or the type of reaction.
Common Names
Some enzymes have common names that do not strictly follow the standard naming convention.
Examples
Sucrase: Enzyme that catalyzes the hydrolysis of sucrose.
DNA Polymerase: Enzyme that catalyzes the polymerization of DNA strands.
IUBMB Classification
Enzyme Commission (EC) Numbers
Established by the International Union of Biochemistry and Molecular Biology (IUBMB).
Provides a comprehensive and systematic classification of enzymes based on the reactions they catalyze.
Six Major Classes
Enzymes are divided into six main classes, each representing a broad type of reaction.
Oxidoreductases
Transferases
Hydrolases
Lyases
Isomerases
Ligases
EC Number Structure
Each enzyme is assigned a unique EC number consisting of four parts (e.g., EC 1.1.1.1):
First Digit: Main class (type of reaction).
Second Digit: Subclass (type of substrate or group transferred).
Third Digit: Sub-subclass (specifics of the reaction).
Fourth Digit: Serial number of the enzyme in its sub-subclass.
The Six Major Classes of Enzymes
Oxidoreductases (EC 1)
Catalyze oxidation-reduction reactions, where electrons are transferred from one molecule (the reductant) to another (the oxidant).
Example: Alcohol dehydrogenase (EC 1.1.1.1)
Transferases (EC 2)
Catalyze the transfer of functional groups (e.g., methyl, glycosyl, acyl groups) from one molecule to another.
Example: Hexokinase (EC 2.7.1.1)
Hydrolases (EC 3)
Catalyze the hydrolysis of various bonds, including ester, glycosidic, peptide, and other bonds, through the addition of water.
Example: Lipase (EC 3.1.1.3)
Lyases (EC 4)
Catalyze the addition or removal of groups to form double bonds or the breaking of bonds by means other than hydrolysis and oxidation.
Example: Pyruvate decarboxylase (EC 4.1.1.1)
Isomerases (EC 5)
Catalyze the rearrangement of atoms within a molecule to form isomers.
Example: Triosephosphate isomerase (EC 5.3.1.1)
Ligases (EC 6)
Catalyze the joining of two molecules with the simultaneous hydrolysis of a diphosphate bond in ATP or another nucleotide.
Example: DNA ligase (EC 6.5.1.1)
Example of Enzyme Classification
Let's classify alcohol dehydrogenase:
EC 1.1.1.1
EC 1: Oxidoreductase (main class)
EC 1.1: Acting on the CH-OH group of donors (subclass)
EC 1.1.1: With NAD+ or NADP+ as an acceptor (sub-subclass)
EC 1.1.1.1: Specific enzyme identifier
Practical Importance of IUBMB Classification
The IUBMB classification system allows for:
Standardization: A consistent way to name and categorize enzymes across different languages and fields of study.
Identification: Easy identification of an enzyme's function based on its EC number.
Research: Facilitating research and development by providing clear and detailed descriptions of enzyme activities.