BLOCKING AGENTS 



107 



TABLE X 



Reagents which may be used for blocking various groups in protein 

 molecules. Reagents which may readily be removed are marked with 

 an asterisk. 



is often possible to block a group, carry out a cytochemical pro- 

 cedure, and then remove the blocking agent by a mild treatment 

 with dilute acid, dilute alkali, dithioglycerol, or a heavy metal. 

 After removal of the blocking agent a further cytochemical pro- 

 cedure may be carried out with the group which has been liber- 

 ated. Thus, for example, NH 2 groups may be protected by 

 treatment with PhSCOCl against a reagent for tyrosine. Then 



