Biochemistry of psa

First described by Wang et al. in 1979 (10), PSA is a single-chain glycoprotein neutral serine protease of240 amino acids secreted by the prostate epithelium and CaP cells (1113). A glycoprotein monomer with a molecular weight of 33,000-34,000, PSA contains 240 amino acids (10-14). Among the many PSA-like kallikreins that have been discovered so far, PSA is named human kallikrein 3 (hK3) (11). PSA is involved in the lysis of seminal coagulum and is one of the predominant proteins present in the prostatic fluid. PSA catalyzes the proteolytic degradation of gel-forming proteins secreted by human seminal vesicles and mediates the progressive activation of sperm motility. Even though PSA has been documented to be present in some nonprostate tissues [e.g., periurethral (15-18) and parotid glands (19) in both men and women, and in about 30% of breast tumor specimens (20)], no significant contribution of PSA from these sources to serum PSA has so far been demonstrated. The importance of PSA as a marker in prostatic diseases comes from the fact that only trace quantities of PSA are detected in the serum of all normal males. Changes in the anatomy of the prostate gland could lead to the increased diffusion of PSA in blood circulation. Thus, elevated serum PSA concentrations can suggest the existence of prostatic diseases like CaP, benign prostatic hyperplasia (BPH), prostatitis (21), and prostatic ischemia (22). Because PSA has not been found yet in any other tissue, it has so far been proved to be a highly specific prostate biochemical marker. PSA is present in the serum of normal men at concentration < 4 ^g/L. Women, who have no prostate, should have no PSA in their serum. However, immunoreactive PSA is detectable in about 5% of women's sera, and this is attributed to a prostate-equivalent organ called Skene's gland (17,18). No diagnostic usefulness of PSA in women has been established.

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