216 THE BIOLOGY OF HYDRA : 1961 



TABLE 5 

 Time required for mouths to close on removal of glutathione 



All experiments were carried out using Hydra starved for one day, and at excess 

 glutathione ( 10"^ M). 



Data from reference 8. 



The following simple experiment demonstrated that glutathione 

 did not act as a "trigger," if a triggered response is defined as one 

 that continues after the initial stimulus is removed. Groups of Hydra 

 were incubated in 10"'' M glutathione for periods varying from 5 to 

 25 minutes (Table 5). At the end of each incubation period, the 

 animals in one drop of glutathione solution, were placed in 30 ml. 

 of a solution of the same composition but lacking glutathione. In 

 all cases the mouths closed in less than one minute (Table 5). The 

 results indicate that glutathione had to be constantly present during 

 the total time of the feeding reflex in order for the response to con- 

 tinue. In addition, since the mouths close repidly on removal of 

 glutathione it is concluded that the equilibrium between glutathione 

 and the receptor is rapidly attained. 



This observation that the continued presence of glutathione is 

 required for the activation of the feeding reflex allows us to formu- 

 late a hypothesis on how glutathione activates the receptor. We 

 visualize the receptor as an inactive protein on the siuface of 

 certain Hydra cells. When that protein combines with glutathione, 

 its tertiary structure is altered, rendering the receptor protein physi- 

 ologically active. The active protein is then capable of either initi- 

 ating, or allowing to go on to completion, the events involved in 

 the receptor-eflFector system. 



These data also indicate that the longer Hydra were exposed 

 to the glutathione, the sooner the mouths closed when glutathione 



