LOCALIZATION OF SEMINAL PLASMA PROTEINASE-INHIBITORS IN HUMAN SPERMATOZOA AS REVEALED BY INDIRECT IMMUNOFLUORESCENCE TECHNIQUE

Acidic extracts of washed, ejaculated human spermatozoa contain, besides acrosin [EC 3.4.21.10], 2 proteinase inhibitors, a trypsin [EC 3.4.21.4]-chymotrypsin [EC 3.4.21.1] (elastase) inhibitor (HUSI-I) and a trypsin-acrosin inhibitor (HUSI-II). Using indirect immunofluorescence, these inhibitors were localized in the spermatozoa. Ejaculated spermatozoa were treated with monospecific antibodies raised in rabbits against HUSI-I and HUSI-II, respectively, and with fluorescein-labeled Ig[immunoglobulin]G from goat directed against the rabbit IgG. If acetone-fixed spermatozoa were used, fluorescence appeared only in a small ring near or at the equatorial segment of the spermatozoa. After prefixation of washed spermatozoa with 0.36% formaldehyde, distribution of both inhibitors in the region of the acrosomal caps was clearly demonstrated. They apparently are attached at the plasma membrane. Obviously, in the case of human spermatozoa the inhibitors are relatively easily detached together with the membrane so that prefixation is necessary to achieve proper localization.