In response to egg activation, PSGP is discharged by exocytosis into the perivitelline space, where it undergo rapid proteolysis into glycotridecapeptides. During fertilization and/or early development the glycotridecapeptides prevent polyspermy or are involved in the formation of a fertilization membrane. Cortical alveoli of immature ovaries. Most sialic acid residues exist in the form of polysialyl groups partly capped with deaminoneuraminic acid. The core of the PSGP protein contains an average of 25 exact tandem repeats of the same glycotridecapeptide, where the Ser and the Thr residues are attachment sites of a polysialylglycan chain. Multiple genes for PSGP are transcribed into multiple mRNAs containing diverged numbers of repeating units.