Ultrastructure of human sperm acrosome and determination of acrosin activity under conditions of semen preservation.

Electron microscopical studies of cryopreserved human spermatozoa show considerable ultrastructural changes of the acrosome in spite of the use of a cryoprotective agent (10% glycerol), as compared with fresh semen and with glycerolated semen before freezing. A nearly complete loss of the plasma membrane and a partial removal of the outer acrosomal membrane with depletion of the acrosomal content is observed whereas the inner acrosomal membrane and the equatorial segment remain intact. Simultaneous determinations of the activity of the proteolytic penetration enzyme acrosin (EC 3.4.21.10) before and after addition of glycerol and immediately after freezing and thawing reveal a significant increase of the extractable acrosin activity in glycerol-treated and in cryopreserved spermatozoa compared with the fresh material. The results indicate an association of the acrosin with the inner acrosomal membrane and/or the equatorial segment.