Characterization of the Proteinase Inhibitors from Bull Seminal Plasma and Spermatozoa

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Abstract
Two acid-stable proteinase inhibitors are present in bull seminal plasma and washed ejaculated bull spermatozoa. Inhibitor I with a MW of about 8700 (estimated by gel filtration) is a very strong inhibitor of bull sperm acrosin (EC 3.4.21.10) but also inhibits bovine trypsin (EC 3.4.21.4) and chymotrypsin (EC 3.4.21.2) and porcine plasmin (EC 3.4.21.7); inhibition of porcine pancreatic and urinary kallikrein (EC 3.4.21.8) was not observed. In this respect inhibitor I resembles the well-known cow colostrum trypsin inhibitor. Inhibitor II with a MW near 6800 (estimated by gel filtration) inhibits bovine trypsin and chymotrypsin, porcine plasmin and pancreatic and urinary kallikrein as well as bull acrosin. The inhibition specificity of inhibitor II is thus very similar to that of the basic inhibitor from bovine organs (Kunitz-type). In view of the inhibition strength and other characteristics, the acid-stable bull seminal inhibitors are not identical with the inhibitor from cow colostrum or bovine lung (organs).