Explains Nomenclature & Classification of Enzymes with examples.

1. ENZYMES:
Nomenclature & Classification
Dr. Rituparna Saha
Assistant Professor
Department of Life Sciences
Subject: Enzymology

2. Enzymes
• Biological catalysts, protein in nature, thermolabile, synthesized by living
cells – substance on which enzyme acts – substrates
• Similarities between inorganic catalysts & enzymes – speed up chemical
reactions, accelerate state of equilibrium, doesn’t change, lowers the
activation energy, formation of intermediate, influenced by external
factors
• Differences between inorganic catalysts & enzymes – nature, source,
operating conditions, specificity, activity regulation, size, turnover rate,
lifespan

3. Enzymes - Characteristics
• Cofactor – Non-protein molecules
• Coenzyme – Organic compounds
• Prosthetic group – Non-protein compounds that bind via covalent or
non-covalent bonds
• Apoenzyme – Non-active enzyme without its cofactor
• Holoenzyme – Enzyme along with its cofactor

4. Enzymes – nomenclature & classification
• Substrate acted upon by the enzyme – carbohydrase, proteinase, lipase,
sucrase, maltase
• Type of reaction catalyzed – isomerase, hydrolase, oxidase, transaminase
• Substrate acted upon & type of reaction catalyzed – succinic
dehydrogenase, L-glutamic dehydrogenase
• Substance that is synthesized – Fumarase
• Chemical composition of the enzyme – only protein = pepsin, trypsin,
amylase; protein + cation = carbonic anhydrase (Zn2+
), tyrosinase (Cu2+
);
protein + organic compound = iron porphyrin enzymes (catalase),
flavoprotein (glycine oxidase)
• Substance hydrolyzed and the group involved – carbohydrate, lipid,
protein-hydrolyzing enzymes

5. IUBMB classification of Enzymes

6. EC numbers

7. EC numbers - Examples
EC 1.9.3.1 – Cytochrome c oxidase
1 = Oxidoreductase
9 = acting on a heme group of donors
3 = with oxygen as acceptor
EC 3.4.11.4 – Tripeptide aminopeptidase
3 = Hydrolase
4 = acts on peptide bonds
11 = cleave off the N-terminal amino acid from a polypeptide