REACTIONS OF FIXATIVES WITH PROTEINS. 2 



53 



TABLE 3 



Diagrammatic representation of the chief reactions of mercuric chloride 

 with proteins, in the presence of excess of mercuric chloride 



The reactions of mercuric chloride with protein are affected by 

 the abihty of mercury to form bonds through subsidiary valencies. 

 For instance, mercuric chloride can in certain circumstances react 

 with ammonia to form a diammine.*"^ This results from the fact 

 that mercury can accept extra electrons from donor atoms. 



HsN^ /CI 



HaN-^ ^Cl 

 Mercuric chloride combined with ammonia 



In Strongly alkaline conditions, the mercuric ion is taken up by 

 the amino-groups of proteins (on the side-chains of lysine and 

 arginine), by bonds of this sort.^^^ The mercury then reacts as 



"? 

 1 



NH 



(CH2)4NH., 



;=o 



Lysine forming part of a protein chain 



though present as mercuric hydroxide. The mercuric ion may 

 perhaps combine in a similar way with the -NH.CO- groups of 

 the protein backbone. Beyond this, the mercuric ions form 



