Acrosin inhibition. Comparisons of membrane-associated and -solubilized enzyme.

Acrosin is an extrinsic membrane proteinase from spermatozoa which functions in the fertilization process. Liposomes were utilized as a model system to determined possible effects of membrane association on acrosin's enzymatic activity. By comparison with solubilized enzyme, liposome-bound acrosin had a substantial reduction in the apparent affinity for "progressive" inhibitors such as leupeptin, lima bean trypsin inhibitor, soy bean trypsin inhibitor, and for a proteinase inhibitor from sperm extracts. In contrast, the liposome-bound and -solubilized enzymes were essentially identical with respect to the binding of benzamidine and p-aminobenzamidine which are competitive acrosin inhibitors. These results suggest membrane association can influence some but not all of acrosin's enzymatic properties.