Lactase is an enzyme important in human digestion, specifically in breaking down lactose, the sugar found in milk and dairy products. Its function is to convert lactose into simpler sugars that the body can readily absorb. Without sufficient lactase, individuals may experience digestive discomfort after consuming dairy.
The Molecular Building Blocks
Lactase is a protein constructed from smaller units called amino acids. These amino acids link together in a specific linear sequence, forming a polypeptide chain. This chain then folds into a precise three-dimensional shape, necessary for the enzyme’s function. The human lactase enzyme, for instance, is initially a long chain of 1,927 amino acids, which undergoes further processing to become its mature form.
The intricate 3D structure of lactase includes a specialized region known as the “active site.” This site is where the enzyme interacts with lactose. The unique arrangement of amino acids within the active site allows lactase to bind specifically to lactose, facilitating the chemical reaction it catalyzes.
How Lactase Functions
Lactase functions as a biological catalyst, accelerating the breakdown of lactose without being used up in the process. Lactose is a disaccharide, meaning it is composed of two simpler sugar molecules linked together: glucose and galactose. The primary role of lactase is to break the bond between these two sugars.
When lactose enters the small intestine, it encounters the lactase enzyme. At the active site, lactase binds to the lactose molecule and, with the help of water, hydrolyzes it. This reaction separates lactose into glucose and galactose. Once broken down, these simpler sugars can be absorbed through the walls of the small intestine and enter the bloodstream, providing energy for the body. If lactase activity is insufficient, lactose remains undigested.
Natural Production and Genetic Basis
In the human body, lactase is primarily produced in the small intestine. Specifically, it is synthesized by specialized cells called enterocytes, which line the intestinal wall and have small, finger-like projections known as microvilli. These microvilli collectively form the “brush border,” where lactase performs its function.
The production of lactase is controlled by the LCT gene, located on chromosome 2. This gene provides instructions for making the lactase enzyme. While all humans are born with high lactase expression, necessary for digesting milk during infancy, in most of the world’s population, the LCT gene’s activity naturally decreases after weaning. This leads to diminished lactase production in adulthood. However, variations in the LCT gene can influence whether an individual continues to produce lactase at high levels throughout life.
Lactase Deficiency and Its Implications
When the small intestine does not produce enough lactase, lactose intolerance can arise. This means the body is unable to fully digest lactose. Common symptoms include abdominal cramps, bloating, gas, nausea, and diarrhea, typically appearing 30 minutes to two hours after eating or drinking lactose-containing foods.
There are several types of lactase deficiency. Primary lactase intolerance, the most common, involves a natural, age-related decline in lactase production after childhood. Secondary lactase intolerance occurs due to small intestine damage from illness, injury, or surgery, temporarily reducing lactase levels. Congenital lactase deficiency is a rare genetic disorder where infants are born with little to no lactase activity.
Management often involves dietary adjustments, such as limiting or avoiding lactose-rich foods, consuming smaller dairy servings, or choosing lactose-free products. Supplemental lactase enzymes, available as tablets or drops, can also be taken before consuming dairy to aid digestion.