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Hydrolases

Hydrolases

For medical students2 min readUpdated 2026-10-10

Hydrolases are a major class of enzymes whose primary function is to catalyze hydrolysis reactions. They cleave strong covalent bonds in various molecules, a process that is always coupled with the obligatory addition of a water molecule directly at the site of chemical bond cleavage.

Reaction typeCleavage of a covalent bond with the addition of water
NomenclatureBased on the substrate target or the cleaved bond type
ClassificationSubclasses are designated according to the hydrolyzed substance
Key factorA water molecule ($H_2O$) is an obligatory participant in the cleavage

What Are Hydrolysis Reactions?

The main function of this enzyme class is to accelerate hydrolysis reactions. During this biochemical process, a covalent bond within a complex substrate molecule is broken. A key feature is that cleavage is physically impossible without the direct participation of a water molecule ($H_2O$).

Water is not merely present in the reaction medium; it is integrated into the process by attaching to the newly formed ends of the molecule precisely where the covalent bond was broken. Consequently, the original complex substance is split into simpler structural components that now incorporate the elements of the water molecule.

Principles of Classification and Nomenclature

In biochemistry, the nomenclature and subdivision of these enzymes follow strict and clear rules. The primary classification criterion is the nature of the substrate—the specific substance targeted by the enzyme's action.

Accordingly, hydrolase names are constructed in two main ways:

Thanks to this universal rule, knowing the precise name of an enzyme allows a specialist to easily determine which molecule or chemical bond it is designed to cleave.

Main Representatives of Hydrolases

The diversity of substrates in the body leads to the existence of many specific enzymes. Among the most important representatives of the hydrolase class are the following groups:

  1. Proteases — enzymes that specialize in breaking down proteins.
  2. Amylases — enzymes that target various carbohydrates.
  3. Nucleases — catalyze the cleavage of nucleic acid molecules.
  4. Esterases — enzymes that break down bonds in esters.
  5. Glycosidases — hydrolyze specific glycosidic bonds.
  6. This class also includes lipases and phosphatases, which perform the hydrolytic cleavage of their respective substrates.

Mechanism Breakdown: The Example of Proteases

To clearly and deeply understand the mechanism of hydrolases, it is helpful to examine a classic biochemical reaction: the hydrolysis of a protein molecule.

In this specific case, an enzyme from the protease group acts as the catalyst. The core of the reaction is the targeted cleavage of the peptide bond, structurally designated as -CO-NH-. This strong covalent bond links individual amino acid residues into a single long chain.

The cleavage of the bond between amino acid residues occurs exclusively with the participation of a water molecule ($H_2O$). The product of this reaction is the formation of shorter peptides. A crucial consequence of this process is the appearance of new functional groups at the ends of the resulting fragments: a free carboxyl group (-COOH) forms on one side, and a free amino group ($NH_2$) on the opposite side.

Mnemonic

To remember the nomenclature rule, use 'Substrate + ase = hydrolase': if the enzyme breaks down a protein, it is a prote-ase; if a carbohydrate (amylose), an amyl-ase. The key condition is the participation of water at the cleavage site.

Frequently asked questions

What class number is assigned to hydrolases in the Enzyme Commission (EC) classification?

According to the Enzyme Commission (EC) classification, hydrolases are assigned to class number 3 (the digit 3). In the enzyme code (EC number), this digit is placed first and unambiguously indicates membership in the hydrolase class. Enzymes of this class catalyze the transfer of functional groups to water, essentially carrying out the cleavage of substrate chemical bonds with the obligatory participation of water.

What coenzymes or prosthetic groups are required for hydrolase activity?

The provided sources do not specify coenzymes or prosthetic groups required for hydrolases as a class. It is mentioned that pyridoxal phosphate (PLP), a vitamin B$_6$ derivative, functions with certain hydrolases, but its requirement is not universal for the class. A prosthetic group is defined as a coenzyme firmly bound to the apoenzyme by covalent bonds.

What is the difference between endopeptidases and exopeptidases within the protease group?

The main difference lies in the localization of the hydrolyzed peptide bond within the peptide chain.

FeatureEndopeptidasesExopeptidases
Site of actionCleave peptide bonds located away from the ends of the chain (internal bonds)Hydrolyze peptide bonds at the ends of the chain: N-terminus or C-terminus
Additional action—Also cleave di- and tripeptides
ExamplesPepsin, trypsin, chymotrypsin, elastaseAminopeptidase, carboxypeptidases A and B
What is an obligatory participant in any reaction catalyzed by a hydrolase?

The obligatory participant is a water molecule ($H_2O$). It chemically attaches to the molecule precisely at the site of covalent bond cleavage in the substrate.

What is the basic principle for naming enzymes in this class?

Their names are formed either based on the cleaved substrate (e.g., proteins — proteases, nucleic acids — nucleases) or according to the type of chemical bond being broken.

What chemical changes occur at the ends of the molecule during protein hydrolysis?

As a result of the peptide bond -CO-NH- cleavage involving water, shorter peptide fragments are formed, featuring newly exposed free carboxyl (-COOH) and amino ($$NH_2$$) groups at their terminals.

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