Prostate-specific antigen, also known as Gamma-seminoprotein, Kallikrein-3, kallikrein-related peptidase 3, Semenogelase, KLK3 and PSA, is a secreted protein which belongs to thepeptidase S1 family and Kallikrein subfamily. KLK3/Kallikrein 3 contains one peptidase S1 domain. KLK3/Kallikrein 3 is a glycoprotein produced almost exclusively by the prostate gland. KLK3/Kallikrein 3 is produced for the ejaculate where it liquifies the semen in the seminal coagulum and allows sperm to swim freely.It is also believed to be instrumental in dissolving the cervical mucous, allowing the entry of sperm. Human KLK3/Kallikrein 3 and human KLK2 are closely related products of the human kallikrein genes KLK3 and KLK2, respectively. Both KLK3/Kallikrein 3 and human kallikrein 2 are produced and secreted in the prostate and have important applications in the diagnosis of prostate cancer. Understanding the mechanism by which genetic variation in KLK3/Kallikrein 3 affects prostate cancer risk has important implications for study of the biological role of KLK3/Kallikrein 3 in prostate tumorigenesis. Prostate-specific antigen, also known as Gamma-seminoprotein, Kallikrein-3, kallikrein-related peptidase 3, Semenogelase, KLK3 and PSA, is a secreted protein which belongs to thepeptidase S1 family and Kallikrein subfamily. KLK3/Kallikrein 3 contains one peptidase S1 domain. KLK3/Kallikrein 3 is a glycoprotein produced almost exclusively by the prostate gland. KLK3/Kallikrein 3 is produced for the ejaculate where it liquifies the semen in the seminal coagulum and allows sperm to swim freely.It is also believed to be instrumental in dissolving the cervical mucous, allowing the entry of sperm. Human KLK3/Kallikrein 3 and human KLK2 are closely related products of the human kallikrein genes KLK3 and KLK2, respectively. Both KLK3/Kallikrein 3 and human kallikrein 2 are produced and secreted in the prostate and have important applications in the diagnosis of prostate cancer. Understanding the mechanism by which genetic variation in KLK3/Kallikrein 3 affects prostate cancer risk has important implications for study of the biological role of KLK3/Kallikrein 3 in prostate tumorigenesis.