Enables peroxidase activity. Acts upstream of or within several processes, including hypochlorous acid biosynthetic process; removal of superoxide radicals; and response to fungus. Located in mitochondrion. Is expressed in several structures, including alimentary system; genitourinary system; hemolymphoid system; integumental system; and skeleton. Human ortholog(s) of this gene implicated in several diseases, including Alzheimer's disease 1; cystic fibrosis; kidney failure (multiple); liver disease (multiple); and lung disease (multiple). Orthologous to human MPO (myeloperoxidase). [provided by Alliance of Genome Resources, Apr 2022]