• Journal of Life Science
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• v.22 no.3
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• pp.387-397
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• 2012

In this study, we focused on myomoduline A (MMA) released from the central nervous system of Aplysia kurodai. The primary structure of MMA is Pro-Met-Ser-Met-Leu-Arg-Leu-$NH_2$. This peptide is the same as that of the myomodulin family peptide found in other mollusks. The purified MMA showed a modulating activity of phasic contraction on the anterior byssus retractor muscle (ABRM) of Mytilus edulis. In order to study the relationship between the structure and biological activity of MMA, we synthesized MMA, Des[$Pro^1$]-MMA, Des[$Pro^1,Met^2$]-MMA, Des[$Pro^1,Met^2,Ser^3$]-MMA, and MME. The amino acid sequences of Des[$Pro^1$]-MMA, Des[$Pro^1,Met^2$]-MMA, and Des[$Pro^1,Met^2,Ser^3$]-MMA were Met-Ser-Met-Leu-Arg-Leu-$NH_2$, Ser-Met-Leu-Arg-Leu-$NH_2$, and Met-Leu-Arg-Leu-$NH_2$, respectively. MMA and synthetic peptides were tested on ABRM in M. edulis as well as muscle preparations in Achatina fulica. At $1{\times}10^{-8}$ M or lower, MMA showed a potentiating effect on phasic contraction of the ABRM, but this peptide had an inhibitory effect at $1{\times}10^{-6}$ M or higher. Both MMA and its analogs stimulated a contractile response on the crop and a relaxed catch-relaxing response on the penial retractor muscle of A. fulica. These results suggest that Met-Leu-Arg-Leu-$NH_2$ in MMA is the minimum structure required for the regulation of the contraction of ABRM, as well as the reproductive and digestive activities of mollusks.

• Journal of Life Science
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• v.22 no.4
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• pp.499-507
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• 2012

Previous work has characterized myomodulin A (MMA, PMSMLRLamide) and myomodulin E (MME, GLQMLRLamide) purified from the central nervous systems of the sea hare, $Aplysia$ $Kurodai$, using the anterior byssus retractor muscle (ABRM) of the mussel, $Mytilus$ $edulis$. The amino acid sequences of MMA and MME were the same as those of the myomodulin family peptide found in other mollusks. In this study, we synthesized MME, its derivatives, and other neuropeptides to investigate the relationship between the structure and biological activity of MME. The primary structures of MME's derivatives, Des[$Gly^1$]-MME, Des[$Gly^1,Leu^2$]-MME, and Des[$Gly^1,Leu^2,Gln^3$]-MME, were LQMLRLamide, QMLRLamide, and MLRLamide, respectively. MMA and synthetic peptides were tested on ABRM in $M.$ $edulis$ as well as muscle preparations in $Achatina$ $fulica$. MME displayed an inhibitory effect on phasic contraction of the ABRM at $1{\times}10^{-9}$ M or higher. MME also had a relaxing effect on the catch-tension of AMRM at $1{\times}10^{-8}$ M. Both MMA and its analogs stimulated a contractile response on the crop and relaxed the catch-relaxing response on the penial retractor muscle of $A.$ $fulica$. These results suggest that MME and its analogs have modulatory effects on various muscles of mollusks. This study has also laid the groundwork for future neural and circuit modulation studies during animal behavioral changes.