Inhibitors of acrosin and granulocyte proteinases from human genital tract secretions.

Human seminal plasma contains two acid-stable proteinase inhibitors, HUSI-II (Mr approximately 6500) and HUSI-I, (Mr approximately 11 000) with different inhibition specificities. The inhibitory activity of HUSI-II is strongly limited to trypsin and acrosin; both enzyme-inhibitor complexes are very stable (e.g. bovine trypsin-HUSI-II complex: Ki = 1 x 10(-10)M; human acrosin-HUSI-II complex: Ki = 2.7 x 10(-10)M). The inhibitor from human seminal plasma HUSI-II may therefore be seen as the natural antagonist of the sperm protease acrosin. In addition to pancreatic trypsin and alpha-chymotrypsin, HUSI-I forms strong complexes with neutral proteases of the lysosome-like granules from human granulocytes, for example, the elastase (Ki = 2.5 x 10(-9)M) and cathepsin G, the chymotrypsin like protease (Ki = 7 x 10(-8)M).