The acrosome of spermatozoa contains many enzymes such as hyaluronidase, non-specific esterase and acrosomal proteinase. It is said that these enzymes contribute to removing cumulus cells, corona cells and zona pellucida, respectively. Concerning the release of the enzymes, non-specific esterase differs from both hyaluronidase and acrosomal proteinase. The spermatozoa release the latter two enzymes after the vesiculation of acrosome; on the other hand, they lose the former enzyme while acrosomes are still kept intact.
To know the cause of this difference, the precise localization of non-specific esterase was investigated on the spermatid of guinea pig testis and the spermatozoa of epididymis by using the histochemical technique. The results showed that the esterase activity was recognized on the acrosomal membrane until step 8 of spermatogenesis (Clermont, 1960), while it was seen only along the plasma membrane, which covered the acrosomal cap region, in late-stage spermatids and spermatozoa.