DETERMINATION OF STRUCTURE OF PROTEINS 89 



Complete Hydrolysis after Treatment with Nitric Acid, Nitrous 



Acid, etc. 



Kossel and Kennaway showed that clupeine could be nitrated and 

 converted into nitroclupeine. Nitroarginine was obtained on hydrolysis. 

 The nitration of arginine occurred in the guanidine part of the mole- 

 cule. Consequently the guanidine grouping will not be used in the 

 linking of amino acids, but will remain free : 



CO NH CH CO NH CH CO NH 



C,H 6 C,H 6 



H,N . (HN)C NH NH C(NH)NH, 



By treating proteins with nitrous acid and then hydrolysing the pro- 

 duct with acid Skraup was unable to separate lysine from the mixture 

 of amino acids. Its e-amino grouping was apparently destroyed 

 by the nitrous acid, so that most probably this grouping is not used in 

 the linkage of amino acids. Further evidence that this amino group is 

 not used in linkage is given by the experiments of Kossel and Cameron 

 upon the action of nitrous acid on sturine by van Slyke's method. An 

 amount of nitrogen was evolved which corresponded very closely to 

 the amount of lysine in the molecule and it corresponded to only one 

 of its two amino groups. 



Kossel and Gawrilow have also shown that the e-amino group of 

 lysine is free and not used in the linkage of the amino acids by the 

 reaction of proteins with formaldehyde. Those proteins containing 

 very little or no lysine only react very slightly or not at all. In general, 

 although the proportion is not exact the more lysine a protein contains 

 the more it reacts with formaldehyde. 



