Nomenclature and IUBMB Classification of Enzymes

• The nomenclature and IUBMB classification of enzymes refers to the systematic method used to name and categorize enzymes based on the chemical reactions they catalyze.
• nomenclature and IUBMB classification of enzymes system is governed by the International Union of Biochemistry and Molecular Biology (IUBMB).

Enzyme Nomenclature

1. 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.

2. Common Names:

   • Some enzymes have common names that do not strictly follow the standard naming convention.

3. Examples:

   • Sucrase: Enzyme that catalyzes the hydrolysis of sucrose.
   • DNA Polymerase: Enzyme that catalyzes the polymerization of DNA strands.

IUBMB Classification

1. 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.

2. Six Major Classes:

   • Enzymes are divided into six main classes, each representing a broad type of reaction.
     • Oxidoreductases
     • Transferases
     • Hydrolases
     • Lyases
     • Isomerases
     • Ligases

3. 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

1. 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)

2. 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)

3. 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)

4. 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)

5. Isomerases (EC 5)

   • Catalyze the rearrangement of atoms within a molecule to form isomers.
   • Example: Triosephosphate isomerase (EC 5.3.1.1)

6. 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.

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