High impact information on speract

• Speract induces calcium oscillations in the sperm tail [1].
• A. punctulata spermatozoa do not respond to speract, a peptide isolated from the jelly layer of Strongylocentrotus purpuratus eggs [2].
• Highly homologous SRCR domains (one, three, or four per polypeptide chain) are found in diverse secreted and cell-surface proteins from humans (e.g., CD5, complement factor I), mice (Ly-1), and sea urchins (speract receptor) [3].
• Changes in FP130 phosphorylation triggered by the egg peptide speract were delayed in microG [4].
• These peptides include resact and speract obtained from eggs and atrial natriuretic peptides (ANP) [5].

Biological context of speract

• Thus, speract induced a slight depolarization in Na+-free seawater with 10 mM K+ but a hyperpolarization with 2 mM K+ [6].
• Evidence presented indicates that speract activates K+ channels in the flagellar membrane and modulates the Na+/H+ exchange activity through resultant changes in membrane potential [6].
• However, K+ permeability is restored upon subsequent elevation of intracellular [Ca2+] (Cai), indicating either that sperm K channels possess an alternate regulatory mode, or that a distinct Ca(2+)-activated K permeability also participates in speract signal transduction [7].
• The peptides showed complete species specificity and analogues of one peptide (speract) caused decreases in enzyme activity coincident with their receptor binding properties [8].
• This study provides tentative identification of sperm Ca channels as downstream targets of cAMP action and indicates that pHi may determine whether cGMP- or cAMP-mediated second messenger pathways predominate in speract signal transduction [9].

Anatomical context of speract

• Speract (Gly-Phe-Asp-Leu-Asn-Gly-Gly-Gly-Val-Gly) or resact (Cys-Val-Thr-Gly-Ala-Pro-Gly-Cys-Val-Gly-Gly-Gly-Arg-Leu-NH2) stimulated the incorporation of 32P into various proteins of isolated spermatozoan membranes in the presence, but not absence, of GTP [10].
• Further support for the activation of K+ channels in the flagella was the 2-5-fold stimulation of K+ efflux induced by speract as measured with a K+ electrode [6].
• Intracellular sodium changes during the speract response and the acrosome reaction in sea urchin sperm [11].
• Retention of the speract receptor by isolated plasma membranes of sea urchin spermatozoa [12].

Associations of speract with other chemical compounds

• An apparent receptor for the egg peptide speract (Gly-Phe-Asp-Leu-Asn-Gly-Gly-Gly-Val-Gly) was identified by covalently coupling a radiolabeled speract analogue to intact spermatozoa and was then purified by DEAE-Sepharose chromatography and preparative gel electrophoresis after solubilization with Lubrol PX [13].
• Sodium-dependent activation of sea urchin spermatozoa by speract and monensin [14].
• Ammonia or speract counteracted the acetic acid inhibition, but speract failed to further stimulate spermatozoa in the presence of ammonia [15].
• That the H+ and K+ efflux in response to peptide was receptor-mediated was confirmed by the use of speract or resact on intact sea urchin spermatozoa, where the peptides were found to stimulate K+ efflux and to reverse the tetraphenylphosphonium inhibition on H+ efflux only in the homologous spermatozoa [6].
• A low molecular weight peptide (speract) associated with sea urchin eggs has been purified to apparent homogeneity by charcoal adsorption, DEAE-Sephacel chromatography, Bio-Gel P-2 filtration, and Dowex AG 50W-X4 chromatography [16].

Analytical, diagnostic and therapeutic context of speract

• These membranes, prepared by nitrogen cavitation and subsequent sucrose gradient centrifugation, retained the capacity to bind [125I]-Bolton-Hunter speract (nonspecific binding was less than 5% of specific binding) [12].
• Stopped-flow fluorometry was used to examine the binding of labeled speract and the intracellular changes in pH (pH(i)) and Ca2+ ([Ca2+]i) it induces in sperm [17].

References