Hydrolase is a group of enzymes that hydrolytically cleaves substrates. Some hydrolases contribute to the normal functioning of the human body, for example, starch-cleaving amylase. Other hydrolases are involved in the development of disease and, like urease, are produced in bacteria.
What is hydrolase?
Hydrolases are enzymes that use water to cleave substrates. The substrate docks with the active site of an enzyme, where interactions between the two units cause the substrate to break into two parts. At the same time, a water molecule (H2O) is split into a single hydrogen atom (H) and an OH group. One part of the substrate attaches to the single hydrogen atom, while the OH group attaches to the other part of the substrate. Accordingly, the product of hydrolases consists of two new compounds. Hydrolases work with various substrates; these include esters, ether peptides, glycosides, acid hydrides, and C-C bonds. Hydrolytic cleavage by hydrolases is reversible. In the EC classification, they represent group 3, which includes several subgroups. The subgroups include, for example, lipase, which cleaves fat, and lactase, which cleaves milk sugar (lactose). A deficiency of lactase leads to intolerance of lactose, which can be reflected in gastrointestinal symptoms when milk is consumed.
Function, effect, and tasks
Hydrolases are abundant in the human body. Amylase is also one of the hydrolases. Amylase is found in saliva and is responsible for the cleavage of starch and other polysaccharides. Polysaccharides are multiple sugars consisting of chains of carbohydrates. Amylase hydrolytically splits these chains, thereby breaking them down into smaller units. This gives rise to the sweet taste that people can taste when chewing bread and other starchy foods. The processing of polysaccharides by amylase represents the first stage of biochemical digestion – after the teeth have mechanically broken down the food during chewing. Kynureninase is found in all tissue types and cleaves alanine. Both the synthesis of nicotinic acid and the breakdown of tryptophan require this step. Tryptophan is an essential amino acid involved in the synthesis of serotonin. Serotonin is an important neurotransmitter (messenger substance). However, the breakdown of tryptophan is also an intermediate step in the synthesis of other substances, for example nicotinamide adenine dinucleotide (NAD). NAD is a coenzyme that participates in numerous biological functions. For example, it supports the work of dehydrogenases and is part of the respiratory chain. Kynureninase contributes not only to the degradation of tryptophan, but also to the synthesis of nicotinic acid. Nicotinic acid or niacin is a vitamin that belongs to the B-complex.
Formation, occurrence, properties and optimal values
The human body forms hydrolases where they are used. For example, the amylase in saliva is formed in the salivary gland, while the pancreas produces pancreatic amylase. Like all enzymes, hydrolases can only work under certain conditions. Above all, the pH value of the environment and the temperature are of great importance for them. Amylase, for example, can only exist at a pH of 3.5 to 9. If the environment deviates from this range, the enzyme denatures. Gastric acid has a pH of 1-1.5 on an empty stomach, making it too acidic for amylase. Gastric acid denatures the protein structure by breaking molecular bonds. The enzyme thus loses its shape and becomes inactive. Therefore, the pancreas must also synthesize amylase and return it to the food pulp at a later stage of digestion. The optimum temperature for amylase is 45 °C; at this temperature amylase works fastest, i.e. it converts the largest amount of substrate. Amylase can also work outside this optimum – but the metabolic rate is somewhat lower. Temperatures that are too high also denature the enzyme and either render it useless or break the protein down into its individual amino acids.
Diseases and disorders
Some hydrolases can help diagnose diseases. For example, doctors can use amylase levels in the ovaries and lungs to diagnose certain forms of cancer.Amalysis levels are conspicuous in cancers in these organs and can thus provide an indication of the presence or spread of neoplasms. A mutation in the KYNU gene leads to a deficiency of kynureninase. The enzyme is involved in various biochemical processes. When there is too little kynureninase in the body, cells cannot synthesize vitamin B3 (also called nicotinic acid or niacin) as usual and hypovitaminosis occurs. Signs of B3 deficiency include dermatitis and inflammation of the oral, gastric and intestinal mucosa. In addition, diarrhea, depression, loss of appetite, concentration problems, sleep disorders and irritability may occur. The deficiency can also cause the disease pellagra. Not only the human organism produces hydrolases. Pathogens such as bacteria can also produce enzymes from this group. One enzyme that can actually harm humans is called urease, which breaks urea into ammonia and carbon dioxide. The ammonia helps the bacteria resist stomach acid. As a result, they can infect the digestive system and cause a number of ailments. The bacterium Helicobacter pylori belongs to this group of pathogens. Among others, Helicobacter pylori triggers type B gastritis, can be responsible for gastric and duodenal ulcers, and can cause gastric carcinoma if chronically infected.
