SPACA1 (also known as SAMP32) is localized to the acrosome of spermatozoa. The acrosome is an organelle transformed from the Golgi apparatus to form a cap over the anterior portion of the spermatozoa head, which contains the sperm nucleus. Mammalian acrosomes contain digestive enzymes that degrade the ovum outer membrane (zona pellucida) to allow fusion of the sperm and ovum nuclei via the acrosomal reaction []. In mammals, the acrosome releases hyaluronidase and acrosin. Antibodies against recombinant SAMP32 inhibits both the binding and the fusion of human sperm to zona-free hamster eggs []. Male mice lacking SPACA1 are infertile, and exhibit globozoospermia-like misformed sperm heads []. SPACA1 content has been reported to be diminished in a comparison of round-headed and normal spermatozoa [].
