Structure, function, and regulation of the enzyme activity of prostate-specific antigen

Prostate-specific antigen (PSA) and human glandular kallikrein 1 (hGK-1) are structurally similar products of the human glandular kallikrein gene locus on chromosome 19 that become selectively expressed by human prostate tissue. PSA is one of the most abundant prostate-derived proteins in the seminal fluid. The mature form of PSA, a single-chain glycoprotein of 237 amino acids, is a serine protease manifesting restricted chymotrypsin-like activity. PSA is mainly responsible for gel dissolution in freshly ejaculated semen by proteolysis of the major gel-forming proteins semenogelin I and II and fibronectin. PSA complexed to α1-antichymotrypsin (ACT) is the predominant molecular form of serum PSA, although complex formation is slow between the purified proteins in vitro. PSA also forms stable complexes with α2-macroglobulin (α2M) in vitro, but as this results in encapsulation of PSA and complete loss of the PSA epitopes, the in vivo significance of this complex formation is presently unclear. A free, noncomplexed form of PSA constitutes a minor fraction of the serum PSA, although serum ACT occurs at large molar excess