9.8.5. Classification and Nomenclature of Enzymes

Thousands of enzymes have been discovered, isolated and studied. Most of these enzymes have been classified into different groups based on the type of reactions they catalyse. Enzymes are divided into 6 classes each with 4-13 subclasses and named accordingly by a four-digit number.

Enzymes are biological catalysts that increase the rate of chemical reactions in living organisms. They are categorized into six main classes based on the type of reaction each enzyme facilitates. Each of these classes can have further subclasses, making it easy for scientists to identify and study specific enzymes. The classification system helps biologists and chemists understand the functions of enzymes and their roles in metabolic processes.

Think of enzymes like different types of workers in a factory. Each worker has a specific job, and they specialize in that task. Just like how some workers might build things (transferases) while others clean up scraps (hydrolases), enzymes work on different reactions in our body. This classification helps researchers quickly find the right 'worker' for the job based on the type of reaction they require.

Oxidoreductases/dehydrogenases: Enzymes which catalyse oxidoreduction between two substrates S and S’ e.g., S reduced + S’ oxidised → S oxidised + S’ reduced.

Oxidoreductases are a class of enzymes that facilitate oxidation-reduction reactions, where one molecule is oxidized (loses electrons) and another is reduced (gains electrons). This is important in biological processes like cellular respiration, where energy is extracted from food.

Imagine a battery: when you charge it, you're essentially reducing it, and when it's used to power a device, it gets oxidized. Similarly, oxidoreductases help rearrange electrons in molecules for energy exchange during metabolic processes.

Transferases: Enzymes catalysing a transfer of a group, G (other than hydrogen) between a pair of substrate S and S’ e.g., S - G + S’ → S + S’ - G.

Transferases are enzymes that move functional groups from one molecule (substrate) to another. This process is vital for synthesizing larger biomolecules, such as when building amino acids or nucleotides, where various functional groups need to be exchanged.

Think of transferases like a schoolyard game of tag, where a player (the functional group) is transferred from one child (substrate) to another. Each time someone gets tagged, they have a new role, just like molecules are transformed in biochemical reactions.

Hydrolases: Enzymes catalysing hydrolysis of ester, ether, peptide, glycosidic, C-C, C-halide or P-N bonds.

Hydrolases are enzymes that catalyze hydrolysis reactions, where a water molecule is used to break chemical bonds in larger molecules. This is crucial for digestion, breaking down proteins into amino acids and carbohydrates into sugars.

Imagine hydrolases as a pair of scissors cutting a long piece of ribbon (the large molecule) into smaller pieces (the smaller molecules). Just as scissors help segment the ribbon into manageable pieces, hydrolases help our bodies digest food.

Lyases: Enzymes that catalyse removal of groups from substrates by mechanisms other than hydrolysis leaving double bonds.

Lyases are enzymes that remove groups from substrates without the addition of water (unlike hydrolases). This removal often leads to the formation of double bonds in the substrate, playing important roles in metabolic pathways.

Think of lyases like sculptors chiseling away at a block of marble. Instead of adding material (like water), they remove pieces to reveal a new shape (the double bond) from the substrate.

Isomerases: Includes all enzymes catalysing inter-conversion of optical, geometric or positional isomers.

Isomerases are enzymes that facilitate the interconversion of isomers, which are compounds with the same molecular formula but different arrangements or structures. This is important in processes like the conversion of glucose into fructose.

Consider isomerases like a chef rearranging ingredients in a dish. Even if the same basic components are used, changing their arrangement can yield a different flavor (isomer).

Ligases: Enzymes catalysing the linking together of 2 compounds, e.g., enzymes which catalyse joining of C-O, C-S, C-N, P-O etc. bonds.

Ligases are enzymes that catalyze the joining of two molecules, typically accompanied by the expenditure of ATP. These enzymes are vital for processes that involve the synthesis of larger biomolecules, such as DNA replication where nucleotides are linked.

Think of ligases as construction workers connecting two pieces of wood together with nails. Just as nails bind the wood pieces firmly, ligases help link smaller molecules into a larger structure.

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