Fine-structural localization of phosphatase activity on the plasma membrane of the rabbit sperm head

The mammalian spermatozoon undergoes a series of maturational changes after leaving the testis. Spermatozoa in the caput epididymidis are not fertilizable (Orgebin-Crist, 1967) but are functional when they reach the cauda. Differentiation of the membranes of caput spermatozoa during epididymal transit was demonstrated by the binding of colloidal iron (Cooper & Bedford, 1971) and Concanavalin A (Gordon, Dandekar & Bartoszewicz, 1975). Exposure to seminal plasma appears to stabilize the surface coat (Gordon et al., 1975), the plasma membrane enzymes (Gordon, 1973), and acrosomal enzymes (Zaneveld, Dragoje & Schumacher, 1972). Spermatozoa become capacitated in the female genital tract, a process which removes seminal substances (Ericsson, 1967; Oliphant & Brackett, 1973) and modifies the lectin binding of the membrane (Gordon et al., 1975). The segment of the plasma membrane overlying the acrosome of spermatozoa from the cauda epididymidis contains a neutral ATPase which is not active in ejaculates (Gordon, 1973) and it was postulated that the enzyme may become competent during capacitation following removal of seminal antigens.