Demonstration of the role of prostate-specific antigen in semen liquefaction by two-dimensional electrophoresis.

Two-dimensional protein profiles of human semen, prostatic fluid, and seminal vesicle fluid were compared to demonstrate changes in the protein composition of human semen before and after liquefaction. Semen specimens were obtained from a volunteer. Prostatic fluid specimens were collected by rectal massage from patients visiting a urology clinic. Samples of seminal vesicle fluid were collected by needle aspiration from isolated seminal vesicles, which were removed at surgery. All specimens were prepared and processed according to the ISO-DALT system for separation of proteins in two-dimensional gels. Following electrophoresis, protein spots in the gels were visualized by silver staining. Prostatic fluid and seminal vesicle fluid showed their characteristic protein profiles. The protein profile of human semen contained specific proteins of both prostatic fluid and seminal vesicle fluid. One major group of proteins in seminal vesicle fluid (Mw 28,000-68,000 daltons), designated as seminal vesicle-specific antigen, was observed in freshly ejaculated human semen, but disappeared from the two-dimensional profile when the ejaculate was allowed to stand at room temperature for 30 min. When prostatic fluid or prostate-specific antigen was mixed with seminal vesicle fluid and incubated at 37C for 30 min, the seminal vesicle-specific antigen also disappeared from the two-dimensional profiles. The findings indicate that seminal vesicle-specific antigen, a group of predominant proteins in seminal vesicle fluid, is the structural component of seminal coagulum, and that prostate-specific antigen is the enzyme which digests seminal vesicle-specific antigen and liquifies semen coagulum.