When sperm reaches the ovum in the oviduct it releases a substances known as antifertilizin. It is an acid protein secreted by the acrosome. At the same time, the ovum releases another chemical substance known as fertilizin. It is a glycoprotein. Fertilizin reacts with the antifertilizin in a manner similar to antigen antibody reaction. The fertilizin-antifertilizin reaction is specific and this makes a path for the sperm to reach the surface of the ovum.
The adhesion of spermatozoon to the egg surface occurs due to the presence of fertilizin molecules in the surface layer of egg cytoplasm, which receive antifertilizin molecules present on the surface of spermatozoon.
Function of Fertilizin:
1. Makes the sperm sticky so that they adhere into clumps.
2. Leads to the capacitation of sperm, enabling it to penetrate the egg surface.
3. Makes sperm to adhere to the surface of egg and ensures fertilization.
4. Clumping or agglutination of sperm thins out the number of spermatozoa around the egg to check the entry of any additional sperm into the egg.