Structural Biochemistry/Enzyme Catalytic Mechanism/Enzyme Classification/Hydrolases

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Hydrolases are a class of enzymes that catalyzes the hydrolysis of a chemical bond. The enzymes disrupt the chemical bond by adding water; this step is known as the acylation step. The following scheme is indicative of a hydrolase enzyme: A–B + H2O → A–OH + B–H.


Hydrolases reactions can be used to cleave many types of chemical bonds. They can be used to cleave peptide bonds to break down proteins and polypeptides. Such reaction involve protease. Other hydrolase reactions can be used to cleave phosphodiester bonds to degrade DNA molecules. Such reaction is performed by restriction enzymes, also known as restrictive endonuclease.

In terms of free energy, it is found that hydrolases forms more entropy and is typically an exergonic reaction.

Hydrolases help induce degradative reactions in the body. For example, during digestion lipases hydrolyze lipids and proteases convert proteins to amino acids. Hydrolases also cleave large molecules into fragments used for synthesis, the excretion of waste materials, or as sources of carbon for the production of energy. In each of these reactions, biopolymers are converted to monomers. Some hydrolases also expel a considerable amount of energy as they act.

One of the most important hydrolases is cholinesterase. Acetylcholine is a potent neurotransmitter for voluntary muscle. Nerve impulses travel along neurons to the synaptic cleft, where acetylcholine stored in vesicles is released, carrying the impulse across the synapse to the postsynaptic neuron and propagating the nerve impulse. After the nerve impulse moves on, the action of the neurotransmitter molecules must be stopped by cholinesterase, which hydrolyzes acetylcholine to choline and acetic acid. Dangerous toxins exist such as the exotoxin of Clostridium botulinum and saxitoxin that interfere with cholinesterase, and a considerable number of nerve agents such as tabun and sarin act by blocking the hydrolytic action of cholinesterase.