Lysozyme is a naturally occurring enzyme that functions as part of the body’s innate immune system. Its discovery is attributed to Alexander Fleming in 1922, who observed its antibacterial effects by chance. This protein acts as a first line of defense against microbial invaders. Found in various organisms, from plants to humans, lysozyme provides a protective barrier against certain types of bacteria.
How Lysozyme Functions
Lysozyme’s primary role is to destroy bacteria by breaking down their cell walls. This action is highly specific, targeting a substance called peptidoglycan, which is a structural component of the cell walls of many bacteria. The enzyme functions by hydrolyzing, or cutting, the bonds between two sugars that form the backbone of the peptidoglycan layer. This process compromises the structural integrity of the cell wall.
The specificity of lysozyme for peptidoglycan can be compared to a key that fits a particular lock. This enzyme precisely recognizes and binds to the peptidoglycan molecule within a cleft in its own structure. Once bound, it catalyzes the cleavage of the glycosidic bonds that hold the bacterial wall together. This action is effective against gram-positive bacteria, which have a thick and exposed peptidoglycan layer.
The internal pressure of the cell is no longer contained, leading to a process called osmotic lysis, where the cell swells and bursts. This rupture ultimately kills the bacterium.
Natural Sources of Lysozyme
Lysozyme is widely distributed throughout nature. In the human body, it is found in high concentrations in several bodily secretions. Tears, saliva, and mucus are all rich in lysozyme, where it acts as a guard against potential pathogens entering the eyes, mouth, and respiratory tract. It is also a component of blood and is present within certain types of white blood cells.
Human milk is another source of lysozyme, containing concentrations thousands of times greater than that found in livestock milk. This high level of the enzyme provides infants with a defense against bacterial infections, particularly those that can cause diarrhea. The lysozyme in breast milk contributes to the development of a healthy gut microbiome in newborns and is an element of the immunity passed from mother to child.
Outside of the human body, the source of lysozyme is hen egg white. In this environment, the enzyme makes up a portion of the total protein content, constituting about 3.5%. Its function here is to protect the developing embryo from bacterial contamination, ensuring the egg remains a sterile environment. The high concentration and accessibility of lysozyme in egg whites have made it the primary source for commercial extraction.
Commercial and Medical Applications
The natural antimicrobial properties of lysozyme have led to its adoption in various commercial and medical fields. In the food and beverage industry, it serves as a natural preservative to prevent spoilage. It is particularly useful in cheesemaking, where it can inhibit the growth of certain bacteria that cause a defect known as “late blowing.” In winemaking, lysozyme is used to control malolactic bacteria, sometimes reducing the need for sulfites.
The pharmaceutical and personal care industries have also incorporated lysozyme into a range of products. It is an active ingredient in some antiseptic throat lozenges and oral sprays designed to combat throat infections. You may also find it in specialized eye drops, where it helps protect against bacterial contamination. Some skin creams and wound dressings are formulated with lysozyme to help prevent infections during the healing process.
Beyond these applications, lysozyme is utilized in veterinary medicine as a feed additive to support gut health in livestock, reducing the reliance on conventional antibiotics. It is also a standard tool in biotechnology laboratories for breaking open bacterial cells to extract DNA, RNA, and proteins for research.