HOWARD M. LENHOFF 215 



using magnesium ions, an ion known to compete with calcium in 

 many biological systems. To show the competitive nature of the 

 magnesium inhibition, our data is expressed in a fashion analogous 

 to the Lineweaver-Burke plot. Here (Fig. 2) we plot the reciprocal 

 of the duration of the feeding reflex against the reciprocal of the 

 calcium concentration. These experiments were carried out in the 

 absence of magnesium, or in 10~^ M MgCL, or in 10~^ M MgCL. 

 The data show that the higher the concentration of magnesium, 

 the greater is the inhibition. Furthermore, as the calcium concen- 

 tration is increased, the magnesium inhibition is completely re- 

 versed. These experiments leave little doubt that magnesium is 

 interfering with the normal function of calcium ions in the feeding 

 reflex. Sodium ions also exhibit similar competitive inhibitory efl^ects 

 (9). However, for a comparable inhibition higher concentrations of 

 sodium ions are necessary. 



At present there is little evidence as to whether the calcium 

 functions at the glutathione-receptor, or in the efl^ector system. (It 

 appears that the trypsin activation of the feeding reflex, which will 

 be described later, also requires environmental calcium, thus favor- 

 ing the involvement of calcium in the effector system.) 



Anions were also found to influence the feeding reflex (Table 

 4 ) . Holding the calcium content constant, the order of effectiveness 

 of the anions in increasing the duration of the feeding reflex was: 

 CI > Br > I = NO:, (10). The relationship of this order to the lyo- 

 tropic series suggests that these ions influence the state of some 

 proteins involved in the feeding reflex. 



From a practical viewpoint, these results point out the necessity 

 of controlling precisely the ionic environment for the quantitative 

 study of the feeding complex. 



COMBINATION OF GLUTATHIONE WITH 

 THE RECEPTOR 



Most of the data just described concerns environmental chem- 

 istry. Now we have to ask questions about the first physiological 

 event of the feeding reflex, the combination of glutathione with 

 the receptor. 



