Demonstration of a new acrosin inhibitor in human seminal plasma.

We have recently described the purification and characterization of a tumor-associated trypsin inhibitor (TATI). Studies on its N-terminal sequence suggested identity with the pancreatic secretory trypsin inhibitor (PSTI) (Huhtala, M.-L., Pesonen, K., Kalkkinen, N. & Stenman, U.-H. (1982) J. Biol. Chem. 257, 13713-13716). I report here the occurrence of a TATI-like activity in human seminal plasma. Concentrations of this inhibitor in seminal plasma varied considerably (4-500 ng/ml, n = 50). In radioimmunoassay the dose-response curves of the new seminal plasma inhibitor and purified TATI were parallel. The similarity between these two inhibitors was demonstrated by gel filtration, reverse phase liquid chromatography and ion-exchange chromatography. By ion exchange chromatography the new inhibitor could be separated from the main seminal plasma trypsin inhibitors. Purified TATI was shown to inhibit human acrosin effectively.