What are hydrolysis reactions
The main function of enzymes in this 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 the cleavage is physically impossible without the direct participation of a water molecule ($H_2O$).
Water is not simply present in the reaction medium, but is integrated into the process: it attaches to the resulting ends of the molecule at the exact point where the covalent bond was broken. Thus, the original complex substance breaks down into simpler structural components that now include elements of the water molecule.
Principles of classification and nomenclature
In biochemistry, the nomenclature and division of these enzymes into subclasses are based on strict and clear rules. The main classification criterion is the nature of the substrate—that is, the specific substance toward which the enzyme's action is directed.
Accordingly, the names of hydrolase enzymes are constructed in two main ways:
- By the name of the substance being cleaved (the substrate).
- By the specific type of chemical bond undergoing hydrolytic cleavage.
Thanks to this universal rule, knowing the exact name of the enzyme, a specialist can easily determine which specific molecule or chemical bond it is designed to break.
Main representatives of hydrolases
The diversity of substrates in the body gives rise to the existence of many specific enzymes. Among the most important representatives of the hydrolase class, the following groups are distinguished:
- Proteases — enzymes that specialize in breaking down proteins.
- Amylases — various carbohydrates serve as targets for these enzymes.
- Nucleases — catalyze the cleavage of nucleic acid molecules.
- Esterases — enzymes that break bonds in esters.
- Glycosidases — hydrolyze specific glycosidic bonds.
- This class also includes lipases and phosphatases, which perform the hydrolytic cleavage of their respective substrates.
Mechanism analysis using proteases as an example
To clearly and deeply understand the mechanism of action of hydrolases, it is advisable to consider a classical biochemical reaction — the hydrolysis of a protein molecule.
In this specific case, an enzyme from the protease group acts as the catalyst. The essence of the reaction boils down to the targeted cleavage of the peptide bond, which is structurally designated as -CO-NH-. This strong covalent bond connects 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 such a reaction is the formation of shorter peptides. The most important consequence of this process is the appearance of new functional groups at the ends of the formed fragments: a free carboxyl group (-COOH) is formed on one side, and a free amino group ($NH_2$) on the opposite side.
Briefly: answers to topical questions
What class number is assigned to hydrolases according to the Enzyme Commission (EC) classification?
According to the Enzyme Commission (EC) classification, hydrolases are assigned the third class number (number 3). In the enzyme code number (EC number), this digit is in the first place and unambiguously indicates belonging to the class of hydrolases. Enzymes of this class catalyze the transfer of various groups to water, i.e., they carry out the cleavage of substrate chemical bonds with the obligatory participation of a water molecule.
What coenzymes or prosthetic groups are required for the functioning of hydrolases?
The provided sources do not specify coenzymes or prosthetic groups mandatory for the functioning of hydrolases as a class. It is mentioned that pyridoxal phosphate (PLP), a derivative of vitamin B₆, functions with enzymes of the hydrolase class, but its mandatory requirement for hydrolases is not stated. A prosthetic group is defined as a coenzyme tightly bound to the apoenzyme by strong 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.
| Sign | Endopeptidases | Exopeptidases |
|---|---|---|
| Site of action | Cleave peptide bonds located away from the ends of the chain, i.e., internal bonds | Hydrolyze peptide bonds from the ends of the chain: the N-terminus or C-terminus |
| Additional action | — | Also cleave di- and tripeptides |
| Examples of enzymes | Pepsin, trypsin, chymotrypsin, elastase | Aminopeptidase, carboxypeptidases A and B |
To remember the essence of nomenclature, use the rule "Substrate + ase = hydrolase": if the enzyme breaks down a protein, it is a prote-ase, if a carbohydrate (amylose) — amyl-ase. The main condition is the participation of water at the site of cleavage.
Class and exam questions
What is an obligatory participant in any reaction catalyzed by a hydrolase?
An obligatory participant is a water molecule ($H_2O$). It chemically attaches to the molecule strictly at the site of the covalent bond rupture in the substrate.
What is the basic principle used to name enzymes of this class?
Their names are formed either on the basis of the cleaved substrate (e.g., proteins — proteases, nucleic acids — nucleases) or by the type of chemical bond being destroyed.
What chemical changes occur at the ends of the molecule during protein hydrolysis?
As a result of the cleavage of the -CO-NH- peptide bond involving water, shorter peptide fragments are formed, at the ends of which free carboxyl (-COOH) and amino groups ($NH_2$) necessarily appear.
What else to study on this topic
- Structural features of the -CO-NH- peptide bond and mechanisms of its cleavage.
- Differences in the action of amylases and glycosidases during carbohydrate hydrolysis.
- Specificity of esterases toward ester molecules.
- Mechanism of action of nucleases on various nucleic acids.
- The role of phosphatases and lipases in cellular hydrolysis processes.
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