Enables serine-type endopeptidase inhibitor activity. Involved in several processes, including negative regulation of blood vessel endothelial cell migration; positive regulation of blood vessel remodeling; and positive regulation of immune response to tumor cell. Acts upstream of or within several processes, including heme export; negative regulation of fibrinolysis; and regulation of transcription from RNA polymerase II promoter in response to iron. Located in endolysosome and phagolysosome membrane. Human ortholog(s) of this gene implicated in thrombophilia due to HRG deficiency and thrombosis. Orthologous to human HRG (histidine rich glycoprotein). [provided by Alliance of Genome Resources, Apr 2022]