May be involved in sperm maturation and/or fertilization. May also be involved in epithelia functions associated with establishing and maintaining gradients of ions or nutrients. Binds 1 zinc ion per subunit. Highly expressed in Leydig cells. Expressed also in cauda epididymidis, vas deferens, convoluted tubules, kidney and the parietal cells of stomach. Not detected on developing spermatocytes or mature sperm. A tripeptide motif (VGE) within disintegrin-like domain could be involved in the binding to egg integrin receptor and thus could mediate sperm/egg binding. The cysteine-rich domain encodes putative cell-fusion peptides, which could be involved in sperm-egg fusion. The conserved cysteine present in the cysteine-switch motif binds the catalytic zinc ion, thus inhibiting the enzyme. The dissociation of the cysteine from the zinc ion upon the activation-peptide release activates the enzyme. Has no obvious cleavage site for furin endopeptidase, suggesting that the proteolytic processing is regulated.