HOWARD M. LENHOFF 225 



of trypsin was inhibited by trypsin inhibitor (Table 9). Thus, the 

 response seems to be a result of the proteolytic activities of these 

 enzymes. Of twenty other purified proteins, only chymotrypsin gave 

 a significant (8 min.) response (12). It does not seem likely that 

 the proteases are acting by releasing reduced glutathione from 

 Hydra because y-glutamyl linkages are rare in proteins, and because 

 furthermore glutamic acid, a specific inhibitor for glutathione (13), 

 does not inhibit the action of trypsin (9) . 



The possible effects of proteases on a whole animal are so numer- 

 ous that it would be difficult at this time to single out any one 

 action that would explain their effect on Hydra. Nevertheless, the 

 important fact remains that proteases do activate a response, and 

 thus a study of their effects might help in arriving at an understand- 

 ing of the actual mechanism. For example, trypsin can activate 

 only an 18-minute response; if glutathione, however, is added to 

 the same Hydra, they respond an additional 17-18 minutes. In con- 

 trast, after a 35 minute response initiated by glutathione, the addi- 

 tion of trypsin has no effect. A mixture of excess glutathione and 

 excess trypsin, interestingly enough, elicits a response equal only 

 to that initiated by glutathione alone. Thus, these preliminary exper- 

 iments indicate that the protease probably activates a series of 

 events common to those activated by glutathione and involving 

 the consumption of limiting substance X (9). Therefore, in Figure 

 5, the arrow indicating the site of action of the protease is drawn 



TABLE 9 

 Activation of feeding reflex by proteases 



Expt. Test Solution t^-tj 



(min.) 



La. 20 /ig./ml. papain 0.1 



b. 20 fig./ml. papain -|- 10'3 M cysteine 19.8 



c. 20 /ig./ml. papain -|- 10'3 M cysteine, boiled 5 min. at 100° 

 2.a. 0.1 mg./ml. trypsin 17.8 



b. 0.1 mg./ml. trypsin -(- 0.1 mg./ml. trypsin inhibitor 



All Hydra were starved for two days. 

 Data from reference 12. 



