210 



THE BIOLOGY OF HYDRA : 1961 



TABLE 2 

 Activators and inhibitors of the feeding reflex 



In confirmation of Cliffe and Waley ( 3 ) , we were able to extend 

 their striking resnlts demonstrating that the sulfhydryl group is not 

 necessary for the action of gkitathione on Hydra and that this group 

 can be altered within certain limits. These workers obtained a posi- 

 tive response in Ilijdm exposed to the lens tripeptide ophthalmic 

 acid (y-glutamyl-«-amino-/]-butyryl-glycine). This tripeptide, as 

 well as nor-ophthalmic acid, activates the feeding reflex in Hydra. 

 Both peptides are identical to glutathione except that they have 

 respectively a methyl or a hydrogen atom instead of the sulfhydryl. 

 We further show that the S-methyl analog of glutathione also acti- 

 vates the feeding response ( 13 ) . 



On the other hand, substitution of large groups for the sulf- 

 hydryl moiety leads to analogs which do not have the right 

 configuration to activate a response. Rather, such analogs 

 (y-L-glutamyl-L-sulphi-alanylglycine, y-L-glutamyl-L-sulpho-alanyl- 



