bild

Prostate-specific antigen complex. Computer model showing a molecule of prostate-specific antigen (PSA) bound to its activating antibody. Also known as gamma-seminoprotein or kallikrein-3 (KLK3), PSA is a glycoprotein that is secreted by the epithelial cells of the prostate gland. It is a constituent of semen, which it liquefies, allowing sperm to swim freely. It is also believed to be instrumental in dissolving the cervical mucus, allowing the entry of sperm to the female's uterus (womb). (KEYSTONE/SCIENCE PHOTO LIBRARY/RAMON ANDRADE 3DCIENCIA)