Speract peptide was first isolated from the jelly layer of a sea urchin (Strongylocentrotus purpuratus) eggs as a sperm-activating peptide. Speract peptide (at sub nanomolar range) stimulates sperm respiration and motility through intracellular alkalinization, transient elevations of cAMP, cGMP, and calcium levels in sperm cells, and transient activation and subsequent inactivation of the membrane form of guanylate cyclase. Speract peptide also acts as a chemoattractant.Sea Urchin: H-Gly-Phe-Asp-Leu-Asn-Gly-Gly-Gly-Val-Gly-OH or H-GFDLNGGGVG-OH