ZP3 and embryonal carcinoma: On the basis of seminal experiments using purified native material (Bleil & Wassarman, 1980a; Bleil, Greve, & Wassarman, 1988; Florman & Wassarman, 1985) as well as recombinant ZP3 expressed in embryonal carcinoma cells (Kinloch, Mortillo, Stewart, & Wassarman, 1991; Z. Williams, Litscher, Jovine, & Wassarman, 2006), it was suggested that binding of sperm to O‐glycans attached to the C‐terminal region of primary receptor ZP3 induces the acrosome reaction, which, in turn, allows acrosome‐reacted sperm to bind to secondary receptor ZP2 (Bleil & Wassarman, 1980a; Bleil et al., 1988).