The zona pellucida, a transparent envelope surrounding the mammalian oocyte, consists of three glycoproteins, ZPA, ZPB and ZPC, and plays a role in sperm-egg interactions. In bovines, these glycoproteins cannot be separated unless the acidic N-acetyllactosamine regions of the carbohydrate chains are removed by endo-b-Galactosidase digestion. Endo-b-Galactosidase-digested ZPB retains stronger spermbinding activity than ZPC. It is still unclear whether ZPA possesses significant activity. Recently, we reported that bovine sperm binds to Man 5 GlcNAc 2 , the neutral N-linked chain in the cow zona proteins. In this study, we investigated the localization of the sperm-ligand active high-mannosetype chain and the acidic complex-type chains in bovine ZPA. Three N-glycopeptides of ZPA, containing an N-glycosylation site at Asn83, Asn191 and Asn527, respectively, were obtained from endo-b-Galactosidase-digested ZPA. Of these glycosylation sites, only Asn527 is present in the ZP domain common to all the zona proteins. The carbohydrate structures of the N-linked chains obtained from each N-glycopeptide were characterized by two-dimensional sugar mapping analysis, while considering the structures of the N-linked chains of the zona protein mixture reported previously. Acidic complex-type chains were found at all three N-glycosylation sites, while Man 5 GlcNAc 2 was found at Asn83 and Asn191, but there was very little of this spermligand active chain at Asn527 in the ZP domain of ZPA.Keywords: glycoprotein; N-linked carbohydrate chain; sperm ligand; zona pellucida; ZP domain.The mammalian oocyte is coated with a transparent matrix called the zona pellucida. This matrix plays various roles in the early phase of fertilization: species-specific sperm binding, blocking polyspermy, and protecting the embryo until implantation [1,2]. The zona is composed of three glycoproteins, called ZPA, ZPB and ZPC in the order of the size of their cDNAs [3], and their carbohydrate chains are responsible for species-specific sperm-zona binding [1,4].In the pig, the carbohydrate structures of O-linked chains of zona protein mixture [5,6] and the acidic and neutral N-linked chains of ZPB/ZPC mixture [7,8] are well characterized. Sperm-binding activity has been ascribed to the O-linked chains of the zona protein mixture [9] or to the neutral N-linked chains obtained from the ZPB/ZPC mixture [8]. We have shown that the triantennary/tetraantennary chains of the ZPB/ZPC mixture possess greater activity than the diantennary chains [10]. The triantennary/ tetraantennary chains of ZPB are localized at Asn220 in the N-terminal region [10]. Moreover, the isolated N-terminal peptide of ZPB including Asn220 has sperm-binding activity [11]. Yurewicz et al. [12] showed that ZPB and ZPC form heterocomplexes that have sperm-binding activity, but that monomeric ZPB or ZPC does not exhibit this activity. These results suggest that ZPC contributes to the expression of the sperm-binding activity of the neutral N-linked chain of ZPB. In ZPC, the triantennary/tetraante...