Prostate Specific Antigen (PSA)

Human prostate-specific antigen (APS) is a kallikrein-like protease present in seminal plasma. It is a single-chain glycoprotein with a molecular mass of about 33 kD that may function normally in the liquefaction of seminal coagulum. Radioimmunoassay of serum levels of this antigen (called PSA in the clinical setting) is useful in the diagnosis and monitoring of prostatic carcinoma. The full-length KLK3 protein contains 261 amino acids. It has a putative signal peptide, followed by a short activating peptide and the protease domain, which includes the catalytic triad of his65, asp120, and ser213. RT-PCR of 35 adult and fetal tissues detected highest expression in prostate. Expression was weak in colon, mammary gland, and parotid, and little to no expression was detected in other tissues examined.