396 



RADIOISOTOPES IN BIOLOGY AND AGRICULTURE 



Aromatic amino acids: tyrosine, phenylalanine, tryptophan. 



Neutral amino acids: alanine, cysteine, cystine, glycine, hydroxyproline, 

 isoleucine, leucine, methionine, proline, serine, threonine, valine. 



A scheme for group separation is illustrated in Fig. 9-9 (2). This pro- 

 cedure is based on removal of the aromatic amino acids with charcoal, 

 followed by isolation of the basic amino acids after adsorption on a 

 carboxylic-type cation exchanger and finally by separation of the neutral 



Amino 



acids 



in 



5% acetic 



acid 



Chorcoal 



Eluted 

 with 

 phenol- 

 ocetic 

 acid 



Aromotic 

 amino acids 



Cation 

 excti. 



icorboxylic! 



Eluted 

 with 

 HCl 



Basic 

 omino ocids 



Cotion 

 exch. 



(sulfonic) 



n 



Eluted 

 with 

 HCl 



Neutral and 

 dicorboxylic 



t 



Dried 



HgO soln. 



of 



neutral 



end 



dicorboxylic 



r 



Anion 

 exch. 



(chloride) 



Neutrol 

 amino 

 acids 



Eluted 

 with 

 HCl 



Dicorboxylic 

 amino 

 acids 



Fig. 9-9. Scheme for separation of amino acids. (From Olof Samuelson, "Ion Ex- 

 changers in Anaiytical Chemistri/," John Wiley & Sons, Inc., New York, 1953.) 



and dicarboxylic amino acids by use of an anion exchanger in the chloride 

 form. 



Another procedure, as illustrated in Fig. 9-10, has been proposed by 

 Winters and Kunin (9) which not only separates the amino acids into the 

 various groups but also resolves the basic amino acids arginine, lysine, and 

 histidine. In principle, the dicarboxylic acids are separated after adsorp- 

 tion on the weakly basic anion exchanger (Amberlite IR-4B), with the 

 neutral and remaining basic acids passing on through. These are put 

 through a carboxylic cation exchanger (Amberlite IRC-50) at pH 7 which 

 retains the arginine and lysine but allows the neutrals and histidine to 



