Derivatives of speract are associated with the eggs of Lytechinus pictus sea urchins.

Two peptides associated with the eggs of the sea urchin, Lytechinus pictus, which stimulate L. pictus but not Arbacia punctulata sperm respiration rates, were purified and their amino acid sequences determined. The peptides (Gly-Phe-Asp-Leu-Thr-Gly-Gly-Gly-Val-Gln and Phe-Asp-Leu-Thr-Gly-Gly-Gly-Val-Gln) were found to be structurally similar to the peptide, speract (Gly-Phe-Asp-Leu-Asn-Gly-Gly-Gly-Val-Gly). Chemical synthesis of the two peptides confirmed their ability to activate sperm respiration. The peptides had equivalent biological activity with half-maximal stimulation of respiration rates and of cyclic nucleotide concentrations occurring at 60 pM and 700 pM, respectively. Addition of the peptides to intact spermatozoa resulted in the rapid appearance of a newly-stained protein on Na X dodecyl X SOl polyacrylamide gels (Mr = 140,000); one-half maximal formation of the Mr 140,000 protein occurred at about 20-100 nM peptide.