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:12626341). Shows antibacterial properties against Pseudomonas aeruginosa (PubMed:12626341). The lactoperoxidase-SCN(-)-H2O2 system shows antibacterial properties against Burkholderia cepacia and Haemophilus influenzae in vitro (PubMed:12626341). Present in mammary and salivary gland secretions and may contribute to airway host defense against infection (PubMed:12626341). 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. Additional isoforms seem to exist. Mammary gland, milk and salivary gland. Found in bronchial submucosal glands. 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.