清水 健

We characterized putative receptors specific for sperm-activating peptide I (SAP-I: GFDLNGGGVG) in spermatozoa of the sea urchin Hemicentrotus pulcherrimus, using both binding and crosslinking techniques. Analysis of the data obtained from the equilibrium binding of a radioiodinated SAP-I analogue [GGGY(I-125)-SAP-I] to H. pulcherrimus spermatozoa showed the presence of two classes of receptors specific for SAP-I in the spermatozoa. The incubation of intact spermatozoa as well as sperm tails or sperm membranes prepared from H. pulcherrimus spermatozoa with GGGY(I-125)-SAP-I and a chemical crosslinking reagent, disuccinimidyl suberate, resulted in the radiolabelling of a 71 kDa protein. The protein appears to be associated with a 220 kDa wheat germ agglutinin (WGA)-binding protein. A cDNA encoding the 77 kDa protein was isolated from a H. pulcherrimus testis cDNA library. The cDNA was 2443 bp long and an open reading frame predicted a protein of 532 amino acids containing a 30-residue amino-terminal signal peptide, followed by the same sequence as the N-terminal sequence of the 77 kDa protein. The amino acid sequence of the matured 71 kDa protein is strikingly similar to the 77 kDa protein of Strongylocentrotus purpuratus (95.5% identical) and also similar to cysteine rich domain of a human macrophage scavenger receptor. Northern blot analysis demonstrated that mRNA of 2.6 kb encoding the 71 kDa protein was expressed only in the testis.

We examined the effects of two egg jelly components, a fucose sulfate glycoconjugate (FSG) and sperm‐activating peptide I (SAP‐I: Gly‐Phe‐Asp‐Leu‐Asn‐Gly‐Gly‐Gly‐Val‐Gly), on the intracellular pH (pHi) and Ca2+ ([Ca2+]i) of spermatozoa of the sea urchin Hemicentrotus pulcherrimus. FSG and/or SAP‐I induced elevations of [Ca2+] and pHi in the spermatozoa at pH 8.0. At pH 8.0, a second addition of FSG did not induced further elevation of the [Ca2+]i or pHi of spermatozoa treated with FSG, but addition or FSG after SAP‐I or of SAP‐I after FSG induced further increases of [Ca2+]i and pHi, At pH 6.6, FSG and/or SAP‐I did not induce significant elevation of the [Ca2+]i, although SAP‐I elevated the pHi, its half‐maximal effective concentration being 10 to 100 pM. At pH 8.0, tetraethyl‐ammonium, a voltage‐sensitive K+‐channel blocker, inhibited induction of the acrosome reaction and elevations of [Ca2+]i and pHi by FSG, but did not affect those by SAP‐I. These results suggest that FSG and SAP‐I activate different Ca2+ and H+ transport systems. Copyright © 1992, Wiley Blackwell. All rights reserved

A sialoglycoprotein and a fucose sulfate glycoconjugate (FSG) were purified from egg jelly of the sea urchin Hemicentrotus pulcherrimus. Sialoglycoprotein which consisted of sialic acid (90%, w/w) and protein (10%, w/w) did not cause induction of the acrosome reaction and sperm isoagglutination. FSG which contained one mol sulfate/mol fucose possessed 2.0 times protein to fucose by weight. The proteins in intact FSG were separated to two major (258 kDa and 237 kDa) and one minor (120 kDa) proteins by SDS‐polyacrylamide gel electrophoresis (SDS‐PAGE) in the presence of 2‐mercaptoethanol (2‐ME) while the proteins could not be separated by HPLC in the presence of 0.1% SDS or SDS‐PAGE without 2‐ME. However, after carboxymethylation of FSG, two major (260 kDa and 240 kDa) proteins and two minor (140 kDa and 135 kDa) proteins were separated from the fucose sulfate moiety by HPLC in the presence of 0.1% SDS or SDS‐PAGE without 2‐ME. When FSG was first carboxymethylated with non‐radioactive iodoacetic acid and then reduced with 2‐ME and finally carboxymethylated with 14C‐iodoacetic acid, the most of radioactivity was detected in 140 kDa and 135 kDa proteins. Carboxymethylted‐FSG was less potent than intact FSG in induction of the acrosome reaction. Fucoidan, a fucose sulfate polymer, did not induce the acrosome reaction. Copyright © 1990, Wiley Blackwell. All rights reserved