Molecule involved in binding of sperm to egg surfaces and procedures for use of this molecule to enhance or decrease potential fertility

A purified polypeptide which provides for initial binding of sperm to oocyte investments and has an active amino acid sequence of SEQ ID NO:12 (Cys-Gln-Ser-Leu-Gln-Glu-Tyr-Leu-Ala-Glu-Gln-Asn-Gln-Arg-Gln-Leu-Glu-Ser-Asn-Lys-Ile-Pro-Glu-Val-Asp-Leu-Ala-Arg-Val-Val-Ala-Pro-Phe-Met-Ser-Asn-Ile-Pro-Leu-Leu-Leu-Tyr-Pro-Gln-Asp-Arg-Pro-Arg-Ser-Gln-Pro-Gln-Pro-Lys-Ala-Asn-Glu-Asp-Val-Cys); or SEQ ID NO:13 (Cys-Glu-Ser-Leu-Gln-Lys-His-Leu-Ala-Glu-Leu-Asn-His-Gln-Lys-Gln-Leu-Glu-Ser-Asn-Lys-Ile-Pro-Glu-Leu-Asp-Met-Thr-Glu-Val-Val-Ala-Pro-Phe-Met-Ala-Asn-Ile-Pro-Leu-Leu-Leu-Tyr-Pro-Gln-Asp-Gly-Pro-Arg-Ser-Lys-Pro-Gln-Pro-Lys-Asp-Asn-Gly-Asp-Val-Cys); or the shorter but biologically active SEQ ID NO:1 and SEQ ID NO:9 (Tyr-Pro-Gln-Asp-Arg-X-Arg-Ser-Gln-Pro-Gln-Pro-Lys-Ala-Asn, where X is Thr or Pro). The polypeptide is useful in improving sperm-egg binding by fresh sperm, restoring sperm-egg binding following a cryopreservation cycle, enhancing fertilizing potential, and producing antibodies to determine fertilizing potential of sperm, determining sperm-binding sites on egg investments, and contraception.