Heme-containing oxidoreductase which catalyzes the conversion of thiocyanate (SCN(-)) into antimicrobial agent hypothiocyanous acid (OSCN(-)) in the presence of hydrogen peroxide (H2O2) (By similarity). Also involved in the conversion of iodide (I(-)) into hypoiodite (IO(-)) in the presence of H2O2 (By similarity). Responsible for the inactivation of a wide range of micro-organisms and hence, important component of defense mechanism (PubMed:10894086). Shows antibacterial properties against several Gram-positive bacteria including some Staphylococcus species and Gram-negative bacteria including E.coli, P.aeruginosa and some Salmonella species (PubMed:10894086). Inhibits the growth of several fungi including A.niger, Trichoderma species, C.cassicola, P.meadii and C.salmonicolor (PubMed:10894086). Does not have anti-fungal activity towards C.albicans and Pythium species (PubMed:10894086). May protect the udder from infection and may promote growth in newborns (PubMed:10894086). May be implicated in airway host defense against infection (By similarity). May contribute to maintaining an appropriate H2O2 cellular level, therefore protecting cells from H2O2-caused injuries and inflammation (By similarity). 2 a phenolic donor + H2O2 = 2 a phenolic radical donor + 2 H2O H(+) + H2O2 + thiocyanate = H2O + hypothiocyanous acid H2O2 + iodide = H2O + hypoiodite Binds 1 Ca(2+) ion per heterodimer. Binds 1 heme b (iron(II)-protoporphyrin IX) group covalently per heterodimer. Inhibited by small molecule methimazole (MMZ). Mammary gland; milk. The lactoperoxidase system is used by the dairy industry for the preservation of raw milk during transportation (PubMed:10894086). Freshly obtained milk is supplemented with thiocyanate and hydrogen peroxide which are used by milk LPO to produce antimicrobial agents (PubMed:10894086). Thiocyanate (SCN(-)) and hypothiocyanite (OSCN(-)) are bound in the distal heme cavity. The iodide ion (I(-)) occupies a position which is stabilized by the interactions with heme moiety, His-226, Arg-372 and Glu-375. Hydrogen peroxide is held between the heme iron and His-226. Belongs to the peroxidase family. XPO subfamily. The drug propylthiouracilin was reported to bind to the distal heme-pockets of LPO (PubMed:25760705). However, the paper was retracted as some concerns were raised about the modeling.