Hydrolase is a class of hydrolytic enzymes that are commonly used as biochemical catalysts utilizing water to break a chemical bond in order to divide a large molecule into two smaller ones. Hydrolases are pivotal for the body since they digest large molecules into fragments for synthesis, excrete waste materials, and provide carbon sources for the production of energy, during which many biopolymers are converted to monomers. Some hydrolases could release energy when they take effect. A number of hydrolases, especially proteases, are connected with biological membranes as peripheral membrane proteins or affixed through a single transmembrane helix. Some others are multi-span transmembrane ones. The names of hydrolases are systematically formed as "substrate hydrolase, while the commonly adopted names are typically in a form of "substratease."

In biochemistry, a hydrolase catalyzes the hydrolysis of a chemical bond like the following reaction:

Figure 1. Hydrolysis reaction catalyzed by hydrolase.

Classification

Hydrolases belong to EC 3 in the EC classification system and can be further grouped into thirteen subclasses on the basis of the bonds they act upon. EC 3.1 represents a kind of enzymes rupturing ester bonds, which are called esterases. Some common esterases include nucleosidases, phosphatases, proteases, and lipases, among which phosphatases cut phosphate groups off molecules. Acetylcholine esterase is a potent neurotransmitter for voluntary muscle and it as one of the most crucial esterases contributes to the transform of the neuron impulse into acetic acid after it degrades acetylcholine into choline and acetic acid. Some dangerous toxins such as the exotoxin and saxitoxin could impede with the action of cholinesterase, and many nerve agents react by hindering the hydrolytic efficacy of cholinesterase. Nucleosidases are capable of hydrolyzing the bonds of nucleotides. Glycerides could be hydrolyzed by lipases, which also make contribution to the breakdown of fats, lipoproteins and other larger molecules into smaller molecules like fatty acids that are used for synthesis and as a source of energy. Hydrolases in EC 3.2 mainly act upon sugars such as DNA glycosylases and glycoside hydrolase. Acetic acid has become a nice intermediate for glycolysis catalyzed by glycosidases that chop sugar molecules into carbohydrates and peptidases hydrolyze peptide bonds. EC 3.3 includes ether bonds destroying enzymes. EC 3.4 covers hydrolases that act upon peptide bonds like proteases and peptidases. For example, acylpeptide hydrolase as a member of the peptidase family could deacetylate the acetylated N-terminus of polypeptides. Some other type of hydrolases comprise enzymes breaking carbon-nitrogen bonds, not peptide bonds, acid anhydrides (acid anhydride hydrolases, including helicases and GTPase), carbon-carbon bonds, halide bonds, phosphorus-nitrogen bonds, sulphur-nitrogen bonds, carbon-phosphorus bonds, sulfur-sulfur bonds, and carbon-sulfur bonds, with EC number sequentially ranging from 3.5 to 3.13.

Various Functions of Various Hydrolases

Hydrolases could participate in a variety of biological procedures due to their diversification of acting position. Hydrolase expressed by Lactobacillus jensenii in the human gut could stimulate liver to secrete bile salts which facilitate the digestion of food. It has been suggested that the activity of bile salt hydrolase commonly found among intestinal microbiota could increase hydrogel-forming potencies of certain bile salts, whose occurrence in physiological conditions of human gut is thought to be able to enhance bacterial potnetiality to colonize the gastrointestinal tract and their survival rate in this specific ecological niche. Furthermore, new information about the activity of bile salt hydrolase in bacteria can be beneficial to more consciously make use of living microorganisms as food additives and also serves as guidance in the development of new medicines for the prevention and treatment of gastrointestinal disorders. Acylpeptide hydrolase found in human erythrocytes could be potentially treated as a biomarker for low dose exposure to organophosphorus in humans. Glycoside hydrolases play unique roles in various biological processes like the metabolism of cell wall, the biosynthesis of glycans, signalling, plant defence, and the mobilization of storage reserves. It has been found that a single residue in plant GH32, equivalent to Asp239 in AtcwINV1, seems to be important for sucrose stabilization in the active site and indispensable in determining the specificity of sucrose donor. The leukotriene A₄ (LTA₄) hydrolase could act upon epoxide in the final step in the biosynthesis of leukotriene B₄ that occupies a position in a variety of acute and chronic inflammatory diseases. LTA₄ hydrolase as a bifunctional zinc metalloenzyme is a significant enzyme in the 5-lioxygenase pathway and possesses a peptide-cleaving activity. Nucleoside hydrolase plays a central role in the purine salvage pathway and also functions as a primary target for the explorations of anti-parasitic drugs.

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Hydrolases