Stimulation of Sperm Respiration Rates by Speract and Resact at Alkaline Extracellular pH

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Abstract
At an extracellular pH of 6.6, a peptide (resact) isolated from the egg-jelly of Arbacia punctulata increased the respiration rates of A. punctulata spermatozoa but did not activate sperm cells from Lytechinus pictus. In contrast, speract (Gly-Phe-Asp-Leu-Asn-Gly-Gly-Gly-Val-Gly) elevated the respiration rates of L. pictus but not A. punctulata spermatozoa. At normal seawater pH (7.6-8.0), egg jelly from A. punctulata, or egg-jelly from L. pictus purified free of speract, inhibited L. pictus sperm respiration rates. Similarly, the egg jelly from L. pictus inhibited the respiration rates of A. punctulata spermatozoa. The jelly component responsible for the inhibition of respiration was nondialyzable. The inhibition of respiration induced by jelly could be reversed by the addition of speract to L. pictus spermatozoa, and by the addition of resact to A. punctulata spermatozoa. Speract stimulated L. pictus sperm respiration half-maximally at .apprx. 1 nM, in the presence of either heterologous or homologous (speract-free) jelly. Monensin A, an ionophore which elevates sperm intracellular pH, reversed the jelly inhibition of respiration. These results demonstrate that 2 peptides associated with eggs (speract and resact) can stimulate sperm motility and metabolism in the face of inhibitory components present in the egg jelly. Additionally, the peptides demonstrate species specificity.