lactoperoxidase

Lactoperoxidase is a heme-containing enzyme of the peroxidase family found in several mammalian secretions, most notably milk, but also saliva and other mucosal fluids. It plays a role in innate defense by contributing to the antimicrobial activity of secretions.

Biochemically, lactoperoxidase catalyzes the oxidation of substrates using hydrogen peroxide as the oxidant. In the presence of thiocyanate (SCN−), it efficiently converts SCN− to hypothiocyanite (OSCN−); in addition, it can oxidize halides such as bromide and iodide to hypobromite and hypoiodite, respectively. The antimicrobial effects are largely attributed to OSCN− and related reactive species, which disrupt microbial membranes and enzymes. The physiologically important lactoperoxidase system in milk comprises lactoperoxidase, thiocyanate, and hydrogen peroxide, and its antimicrobial efficacy is favored at milk pH values near neutrality.

Structural and biochemical properties include its status as a monomeric, glycosylated protein of roughly 70–80 kDa with a heme prosthetic group. The enzyme exhibits optimal activity around neutral pH and is relatively stable under collected milk storage conditions. It can be inhibited by classical peroxidase inhibitors such as cyanide or azide, and its activity can be modulated by ionic strength and temperature.

Applications and significance extend to dairy technology, where the lactoperoxidase system has been used to extend the shelf life of raw milk and dairy products by providing natural antimicrobial protection. The enzyme and the system are also studied for potential therapeutic and food-ingredient uses due to their broad-spectrum antimicrobial properties.