Heme-containing oxidoreductase which catalyzes the conversion of thiocyanate (SCN(-)) into antimicrobial agent hypothiocyanous acid (OSCN(-)) in the presence of hydrogen peroxide (H2O2) (PubMed:5338806) (Probable). Also involved in the conversion of iodide (I(-)) into hypoiodite (IO(-)) in the presence of H2O2 (PubMed:354515) (Probable). Responsible for the inactivation of a wide range of micro-organisms and hence, important component of defense mechanism (PubMed:5338806, PubMed:354515). The lactoperoxidase-SCN(-)-H2O2 system shows antibacterial properties against some streptococci strains (PubMed:5338806). The lactoperoxidase-I(-)-H2O2 system shows antibacterial properties against E.coli (PubMed:354515). May protect the udder from infection and may promote growth in newborns (By similarity). 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. Mammary gland; milk. Thiocyanate (SCN(-)) and hypothiocyanite (OSCN(-)) are bound in the distal heme cavity (PubMed:19167310, PubMed:19339248). The iodide ion (I(-)) occupies a position which is stabilized by the interactions with heme moiety, His-226, Arg-372 and Glu-375 (PubMed:33882424). Hydrogen peroxide is held between the heme iron and His-226 (PubMed:33882424). Belongs to the peroxidase family. XPO subfamily.