104 



CYTOCHEMISTRY OF PROTEINS 



The details of the procedure necessary for using some of these 

 nitro compounds have been worked out together with L. G. Bell 

 and A. Loveless. The basic procedure is as follows: 



1. Sections are placed for 1 hour in a suspension of 0.5 milliliter of 

 dinitrofluorobenzene and 1 gram of sodium bicarbonate in 100 milliliters 

 of 70 percent alcohol. Under these conditions linkage of the dinitrofluoro- 

 benzene to tyrosine, histidine, NH2 groups, and SH groups may occur. 



2. The sections are washed in three changes of 70 percent alcohol, 5 

 minutes in each change, to remove uncombined dinitrofluorobenzene. 



3. The sections are then treated for 2 minutes with a solution of 

 chromous chloride in 0.1 N hydrochloric acid. This reduces the nitro 

 groups of the dinitrofluorobenzene which is linked to various groups in 

 the section (i.e., R-N0 2 -» R-NH 2 ). 



TABLE VIII 



Some nitro reagents, and groups for the localization of which these 

 reagents may be particularly useful. 



N0 2 



N0 2 



N0 2 



NH, 



NOs 



N0 2 



N0 2 



>N0 2 



>NCO 



>CH 2 Br 



>AsO 



Tyro- 

 sine 



+ 



+ 



>NH-COCH 2 I 



>0-CO-CH 2 I 



>COCl 



SH 



+ 



+ 



NIL 



+ 



+ 



CO2H 



CHOH 



+ 



+ 



+ 



+ 



+ 



+ 



