178 



I. B. WILSON 



number of series of compounds but the series I took are derivatives (Table 2) 

 of choline and tetramethyl ammonium ion (Wilson, 1952). We have gone down 

 the line and removed one methyl group each time to see the effect of replacing 

 a methyl group with a hydrogen atom. 



The first thing we notice in both series is that whether one has the full 

 complement of methyl groups or whether one group is removed makes very 

 little, if any, difference in the binding. 



However, as one proceeds further, large differences occur. One methyl group 

 on the average makes a change of a factor of about 7 in the binding. That 

 the presence of four groups or three groups makes no difference in binding 

 can be interpreted in the following way: 



The quaternary ammonium ions have a tetrahedral structure, that is, they 



TABLE II 

 Inhibitory potency of methylated ammonium ions 



The concentration necessary to produce 50 per cent inhibition when the acetylcholine 

 concentration is 4 X 10^^ M. 



