Lactoperoxidase is a natural defense enzyme found in various organisms, including humans. It is present in a wide range of biological fluids, where it acts as a protective agent. It catalyzes reactions to produce compounds that help maintain a balanced microbial environment.
Where Lactoperoxidase is Found
Lactoperoxidase is found in various bodily secretions. It is present in significant concentrations in milk, especially colostrum and breast milk, protecting newborns from pathogens. The enzyme is also a component of saliva, contributing to oral health by regulating mouth microorganisms. Tears contain lactoperoxidase, providing a protective layer for the eyes. It is also detected in other mucosal glands and secretions, including those in the lungs, bronchi, and nose, defending against airborne microbes.
How Lactoperoxidase Protects
Lactoperoxidase protects through a mechanism known as the “lactoperoxidase system” (LPS). This system involves three components: the lactoperoxidase enzyme, hydrogen peroxide (H2O2), and thiocyanate ions (SCN-). Lactoperoxidase catalyzes the oxidation of thiocyanate ions by hydrogen peroxide, forming hypothiocyanite (OSCN-). This hypothiocyanite is the main antimicrobial compound produced by the system.
The hypothiocyanite generated by the LPS has broad-spectrum antimicrobial properties, impacting bacteria, viruses, and fungi. It primarily functions by inhibiting microbial growth rather than directly killing all pathogens. Hypothiocyanite oxidizes the sulfhydryl (-SH) groups of various microbial enzymes and proteins, altering their function. This interference can disrupt essential metabolic processes within microorganisms, such as glycolysis, respiration, and nutrient transport.
The inhibitory effect of hypothiocyanite on bacterial metabolism and growth is more effective than hydrogen peroxide alone. While hydrogen peroxide can be bactericidal at high concentrations, the LPS is more efficient at inhibiting microbial activity even with lower levels of hydrogen peroxide. This system helps regulate microbial populations without harming mammalian cells. The LPS action can be reversed by adding sulfhydryl compounds, which reduce oxidized sulfhydryls and excess hypothiocyanite, allowing inhibited cells to recover.
Applications of Lactoperoxidase
The antimicrobial properties of lactoperoxidase have led to its use in various applications beyond its natural biological role. One area is food preservation, particularly in the dairy industry. Activating the lactoperoxidase system by adding hydrogen peroxide and thiocyanate can extend the shelf life of refrigerated raw milk. This enzyme is also used as an indicator of overpasteurization in milk due to its heat resistance.
Lactoperoxidase also finds use in oral hygiene products. It is included in toothpastes and mouthwashes, as it helps maintain a healthy oral microflora. Products containing the lactoperoxidase system can reduce cariogenic bacteria, such as Streptococcus mutans, and help prevent plaque formation and gingivitis. The enzyme’s ability to oxidize salivary thiocyanate ions contributes to its protective effect against dental caries.
Beyond food and oral care, lactoperoxidase is being explored for applications in other fields. It has potential uses in cosmetics and ophthalmic solutions due to its antimicrobial and antiviral properties. Research also explores its use in animal feed and for therapeutic applications, including wound treatment and as an agent against tumors and viruses. Bovine milk is a common industrial source for this enzyme due to structural and functional similarities between bovine and human lactoperoxidase.