Beta-galactosidase

Beta-galactosidase is a large bacterial enzyme that is found in many living organisms. It is often also referred to as β-galactosidase, lactase, beta-gal, or β-gal. Enzymes like beta-galactosidase create chemical reactions that help the body perform many of its essential tasks. Beta-galactosidase specifically plays a number of small, but necessary, roles in the human body. Most important, it breaks down lactose into glucose and galactose so that they can be used in glycolysis. Beta-galactosidase also breaks down lactose and reconnects the separated pieces in a new configuration that ultimately forms a similar sugar molecule called allolactose. While it is present at regular levels in most people, some individuals may be beta-galactosidase deficient. Such deficiencies often have observable medical consequences. The most notable of these is lactose intolerance, which arises from a lack of beta-galactosidase in the upper intestinal tract. Other potential medical consequences include conditions like galactosialidosis and Morquio syndrome B.

Background

Beta-galactosidase is one of many enzymes that are produced naturally in the human body. An enzyme is a type of protein found within cells. Enzymes create chemical reactions and increase the rate at which those reactions occur. Different enzymes assist the body in carrying out different critical tasks. Some of the various tasks in which enzymes play a critical role include muscle-building, the destruction of toxins, and the breaking down of food during the digestive process. Each enzyme’s specific function is directly related to its shape. An enzyme’s shape can be altered by heat, disease, or exposure to certain chemicals. When body temperature rises above normal levels due to a fever, the structure of enzymes can begin to break down. Similar breakdowns may occur in the event of a disease like pancreatitis or in the presence of chemicals called inhibitors that interfere with an enzyme’s ability to start a chemical reaction. When an enzyme’s structure is altered, it stops working. This, in turn, leads to a breakdown of the broader processes that enzymes support.

Digestive enzymes are among the most important enzymes in the body. Most digestive enzymes are produced in the pancreas, stomach, and small intestine. Some are also produced by other parts of the digestive system, such as the salivary glands. Wherever they are produced, digestive enzymes help the body to break down food molecules so that they can be converted to energy. There are three main types of digestive enzymes: amylase, protease, and lipase. Amylase enzymes break starches and carbohydrates down into sugars. It is secreted from both the salivary glands and the pancreas. Amylase levels are sometimes measured in order to diagnose pancreatic or other digestive tract diseases. Protease enzymes break proteins down into amino acids. The most common proteases include carboxypeptidase A, carboxypeptidase B, chymotrypsin, pepsin, and trypsin. Lipase enzymes break fats and oils called lipids down into glycerol and fatty acids. While most lipase is produced by the pancreas, smaller amounts are also produced in the mouth and stomach. Some other common enzymes include maltase and sucrase. Maltase is an enzyme secreted by the small intestine that breaks down malt sugar. Sucrase is another enzyme secreted by the small intestine that breaks sucrose down into the simple sugars fructose and glucose.

Overview

When considered alongside other digestive enzymes, beta-galactosidase is typically referred to as lactase. Beta-galactosidase’s main role in digestion is to break down lactose, a sugar found in dairy products. When this happens, the original lactose is broken down into the simple sugars glucose and galactose so that they can be used in glycolysis. Glycolysis is the crucial first step in breaking down glucose so the body can extract energy for cellular metabolism. Similarly, beta-galactosidase can also separate lactose into pieces and then reconnect them in a different configuration so that they form allolactose. Allolactose is a sugar molecule that helps switch on the lac genes, a special set of genes that encode a membrane protein called lactose permease. Lactose permease is a transmembrane pump that allows a cell to take in lactose.

Aside from the role it plays in digestion, beta-galactosidase also functions as a marker gene. A marker gene is a special gene used to determine whether or not a particular nucleic acid sequence has been inserted into a person’s deoxyribonucleic acid (DNA). As a marker gene, beta-galactosidase is specifically used to monitor gene expression, which is the process through which information from a gene is used in the creation of a functional gene product such as ribonucleic acid (RNA) or protein.

Because of the important role the enzyme plays in the human body, people who are beta-galactosidase deficient may experience medical complications of varying severity. The most common problem associated with beta-galactosidase deficiency is lactose intolerance. Lactose intolerance is a condition that arises when beta-galactosidase is not present in the upper intestinal tract. When there is no beta-galactosidase in the tract, lactose is neither broken down nor absorbed as it should be and is instead allowed to move into the lower intestinal tract. The subsequent fermentation of lactose in the lower intestinal tract leads to the release of carbon dioxide, which in turn causes severe intestinal cramps.

Beta-galactosidase deficiency can also lead to more serious conditions like galactosialidosis or Morquio syndrome B. Galactosialidosis is a lysosomal storage disorder, which means that it is caused by an accumulation of undigested or partially digested macromolecules. The symptoms of galactosialidosis vary depending on the age of the patient. Early infantile galactosialidosis can result in problems like hydrops fetalis, inguinal hernia, or hepatosplenomegaly. Abnormal bone development and coarse facial features are also common. Severe cases can even cause fatal complications. The symptoms of later infantile galactosialidosis are generally less severe and may include short stature, heart valve problems, or dysostosis multiplex. Hearing loss or intellectual disability may also occur. Adult galactosialidosis is marked by difficulty coordinating movements, muscle twitches, seizures, and progressive intellectual disability. Morquio syndrome B is a rare inherited birth defect and a progressive disease that worsens as a child grows older. Children with Morquio syndrome B are prone to developing a pronounced curvature of the spine, cloudy corneas, heart murmur, inguinal hernia, liver enlargement, or a loss of nerve function below the neck. Other symptoms include short stature, abnormal bone development, a bell-shaped chest, hypermobile joints, knock-knees, large head, widely-spaced teeth, coarse facial features, or heart and vision problems.

Bibliography

“Beta-Galactosidase.” Marker Gene Technologies, 2018, www.markergene.com/beta-galactosidase-substrates. Accessed 27 June 2019.

“Beta-Galactosidase, Leukocytes.” Mayo Clinic Laboratories, 2019, neurology.testcatalog.org/show/BGA. Accessed 27 June 2019.

Bolen, Barbara. “Types and Functions of Digestive Enzymes.” VeryWell Health, 10 Jan. 2019, www.verywellhealth.com/what-are-digestive-enzymes-1945036. Accessed 27 June 2019.

“Galactosialidosis.” NIH: Genetic and Rare Diseases Information Center (GARD), 16 May 2011, rarediseases.info.nih.gov/diseases/3953/galactosialidosis. Accessed 27 June 2019.

Goodsell, David. “Beta-Galactosidase.” PDB-101, June 2016, pdb101.rcsb.org/motm/198. Accessed 27 June 2019.

“Morquio Syndrome.” Children’s Hospital of Philadelphia, 2018, www.chop.edu/conditions-diseases/morquio-syndrome. Accessed 27 June 2019.

“Morquio Syndrome B.” NIH: Genetic and Rare Diseases Information Center (GARD), 2019, rarediseases.info.nih.gov/diseases/3786/morquio-syndrome-b. Accessed 27 June 2019.

Roland, James. “Why Are Enzymes Important?” Healthline, 15 Jan. 2019, www.healthline.com/health/why-are-enzymes-important. Accessed 27 June 2019.