ABSTRACT
Intrigued by similar specificities of the hydra feeding receptor and γ-glutamyl transferase activity toward GSH, we examined the possibility that these two GSH-binding activities might reside in the same protein. We find that the two activities differ in specificity toward the γ-glutamyl moiety of GSH. The hydra transferase recognizes L-azaserine, L-GlU, D-GlU and L-Gln. The feeding receptor recognizes only L-GlU and L-Gln; L-azaserine and D-GlU have no effect. L-azaserine, known to bind covalently to the γ-glutamyl donor site of mammalian transferase, irreversibly inactivates hydra transferase activity. The transferase affinity label, however, has no effect on the GSH-stimulated feeding response, permitting us to demonstrate that these two activities have different GSH recognition sites and appear to reside in different proteins.
