Seminal plasma proteins of fertile and infertile men analyzed by two-dimensional electrophoresis.

Sperm-free seminal plasma from seminal fluid ejaculate of fertile and infertile men obtained in the presence and absence of aprotinin (500 kallikrein inhibitor units per milliliter) was analyzed by two-dimensional electrophoresis followed by silver staining. To evaluate postliquefaction proteolytic breakdown of seminal plasma proteins, protease inhibitors were added to the semen at 15, 30, and 60 minutes after ejaculation. Most seminal plasma proteins in normospermic men (n = 4) had molecular weights of 30,000 to 70,000 and were similar to those present in serum. The major non-serum protein in seminal plasma of all men was a basic product with an approximate molecular weight of 40,000. A group of proteins (molecular weights = 20,000 to 23,000) in seminal plasma analyzed immediately after liquefaction was detected in oligospermic men (n = 4) but not in normospermic men (n = 4) or azoospermic men (n = 4). When protease inhibitor was added to normospermic semen at greater than or equal to 15 minutes after liquefaction, these proteins (molecular weight = 20,000 to 23,000) and another group of proteins (molecular weights = 40,000 to 43,000) were readily identifiable but were further enhanced in the absence of protease inhibitors. These findings suggest that oligospermic men may have accelerated proteolysis of sperm or seminal plasma proteins that may contribute to subfertility.