This document discusses the classification and nomenclature of enzymes. It notes that enzymes are proteins that catalyze chemical reactions without being consumed. There are several ways enzymes can be named, including by the type of reaction they catalyze (using a suffix like -ase), their substrate, source, regulation, or randomly. The document then describes the systematic classification system developed by the International Union of Biochemists which groups enzymes into six major classes based on the type of reaction catalyzed and assigns each an Enzyme Commission (EC) number for identification.

1. Classification of
enzymes
Namrata Chhabra
M.D. Biochemistry
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2. • Biologic polymers that catalyze the chemical reactions
• Enzymes are neither consumed nor permanently altered because of
their participation in a reaction
• Except for catalytic RNA molecules, or ribozymes, enzymes are
proteins in nature.
• In addition to being highly efficient, enzymes are also extremely
selective catalysts.
Enzymes- Introduction
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3. Nomenclature of enzymes
a) Based on the type of reaction catalyzed (followed by the suffix –ase)
b) Based on the nature of substrate
c) Based on the source of enzyme
d) Based on its regulation
e) Trival names
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4. Nomenclature of enzymes
Based on the type of reaction catalyzed (followed by the suffix –ase)
• Dehydrogenase
• Protease
• Isomerase
• Reductase
• Transferase
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5. Nomenclature of enzymes
Based on the nature of substrate
• Glucokinase
• Hexokinase
• Xanthine oxidase
• Alcohol dehydrogenase
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6. Nomenclature of
enzymes
Based on the source of
enzyme
• Pancreatic lipase
• Gastric lipase
• Salivary amylase
• Muscle phosphorylase
• Hepatic phosphorylase
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7. Nomenclature of enzymes
Based on its regulation
• Hormone specific lipase
Random names
• Trypsin
• Pepsin
• Thrombin
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8. Systematic Names of enzymes
• The International Union of Biochemists (IUB) classification
• Each enzyme has a unique name and code number that identifies the
type of reaction catalyzed, and the substrates involved.
• Enzymes are grouped into six classes.
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9. Class-1- Oxidoreductases
The oxidoreductases catalyze the transfer of reducing
equivalents(hydrogen and electrons)from one redox system to another.
Examples: Dehydrogenase, oxidase, oxygenase, hydro peroxidase
• Lactate dehydrogenase
• Alcohol dehydrogenase
• Aldehyde dehydrogenase
• Xanthine oxidase
• Cytochrome oxidase
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10. Reaction catalyzed by dehydrogenase
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11. Class 2- Transferases
The transferases catalyze the transfer of other groups from one
molecule to another.
Oxidoreductases and transferases generally require coenzymes.
Examples:
• Amino transferase
• Glucosyl transferase
• Methyl transferase
• Phospho transferase
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12. Reaction catalyzed by transferase
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13. Class 3- Hydrolases
The hydrolases cause cleavage of bond using water.
Examples:
• Protease
• Peptidase
• Glycosidase
• Phosphatase
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14. Reaction catalyzed by hydrolase
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15. Class 4 Lyases
• The Lyases catalyze reactions involving either the cleavage or
formation of chemical bonds (also known as synthases)
• with double bonds either arising or disappearing
• Cleavage of bond does not require water.
• Lyases usually break C-C, C-O, C-N, or C-S linkages.
Examples:
Fumarase, Arginosuccinase, glutamate decarboxylase
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16. Reaction
catalyzed by
Lyase
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17. Class 5- Isomerases
• The isomerases move groups within a molecule, without changing
the gross composition of the substrate.
Examples:
• Epimerase
• Aldose ketose isomerase
• Mutase
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18. Reaction catalyzed by Isomerase
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19. Class 6- Ligases
• The ligation reactions catalyzed by ligases (“synthetases,” class 6) are
energy-dependent and are therefore always coupled to the hydrolysis
of nucleoside triphosphates.
Examples:
• DNA Ligase
• Pyruvate carboxylase
• Acetyl Co A carboxylase
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20. Reaction catalyzed by Ligase
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21. Enzyme Commission number (EC number)
• Each enzyme is entered in the Enzyme Catalogue with a four-digit
Enzyme Commission number (EC number).
• The first digit indicates membership of one of the six major classes.
The next two indicate subclasses and sub-subclasses.
• The last digit indicates where the enzyme belongs in the sub-subclass.
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22. Enzyme Commission number (EC number)
• The IUB name of hexokinase is ATP:D-hexose 6-phosphotransferase
E.C. 2.7.1.1.
• This name identifies hexokinase as a member of class 2 (transferases),
subclass 7 (transfer of a phosphoryl group),
• sub-subclass 1 (alcohol is the phosphoryl acceptor),
• and "hexose-6" indicates that the alcohol phosphorylated is on
carbon six of a hexose.
• However, it is still called as hexokinase.
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24. Thank you
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