ADAM24 (testase 1; MEROPS identifier M12.227) is a membrane-anchored protein on the surface of mature sperm. Unusually for an ADAM protein, activation by removal of the propeptide occurs on the cell surface, as sperm transit the caput epididymis, rather than intracellularly. ADAM24 is also phosphorylated at its cytoplasmic tail, leading to the proposal that the peptidase is important for sperm penetration of the zona pellucida, because sperm protein kinase C is activated during the acrosome reaction []. Knockout of the ADAM24 gene in mice leads to reduced fertility, and an increase in the number of polyspermic embryos [].
