The function of EPPIN (epididymal peptidase inhibitor, ENSG00000101448) is as follows. Serine protease inhibitor that plays an essential role in male reproduction and fertility. Modulates the hydrolysis of SEMG1 by KLK3/PSA (a serine protease), provides antimicrobial protection for spermatozoa in the ejaculate coagulum, and binds SEMG1 thereby inhibiting sperm motility. {ECO:0000269|PubMed:15229136, ECO:0000269|PubMed:17644992}.