Action of Glutamic Acid and Glutathione Analogues on the Hydra Glutathione-Receptor

Abstract

REDUCED glutathione (GSH) is known to activate surface receptors of Hydra, resulting in the co-ordinated feeding reflex¹. Loomis's demonstration that asparthione (β-aspartylcysteinylglycine) did not activate the feeding reflex suggests that the γ-glutamyl moiety is essential for the action of GSH¹. Furthermore, the demonstration by Cliffe and Waley that ophthalmic acid (γ-glutamyl-α-amino-n-butyrylglycine) activated the feeding reflex shows that the sulphydryl group is not necessary for the action of GSH on Hydra ². The present work was undertaken to characterize further the structural features of the tripeptide which are necessary for the activation of the GSH-receptor. In this series of experiments we demonstrate that either glutamic acid or glutamine act as competitive inhibitors of GSH. In addition, analogues of the GSH tripeptide were found either to activate or inhibit competitively the feeding reflex, depending on the size of the group substituted for the thiol.