3h2 



CYTOCHEMICAL TESTS ON EMBRYOS 



H. TEST FOB THE -SH GROUPS : 



The following test gives a stable red coloration in the presence of the tri- 

 peptlde glutathione. According to Serra (19i;6): "it is possible not only to 

 demonstrate the existing -SH groups but also to reduce SB groups to SH groups by 

 means of a pre-treatment of the naterials with a solution of 10^ KCN for 10 

 minutes." Of course, the arginine test is also positive for the -SH group pro- 

 teins. An intense reaction for protein -SH presumably demonstrates the existence 

 of active metabolic and synthetic changes in the proteins (Brachet, 19i4-0). Pro- 

 tein denaturation involves an unfolding of polypeptide chains and an increase in 

 -SH reacting groups. Hence, a positive -SH reaction might indicate either an 

 active synthesis or a breakdown of proteins. The procedure follows: 



a. Fix tissues for no more than h hours at room temperature in 10^ formaldehyde. 

 Rlnae in distilled water. 



b. Immerse tissues or sections in 51^ aqueous zinc acetate - 50 seconds. Rinse 

 in distilled water. 



c. Treat with 10^ aqueous solution sodium nitroprusside containing 2^ concen- 

 trated ammonia. Brilliant red color develops within 5 minutes. Wash in 

 distilled water and mount in glycerine. 



The glutathione is partially soluble, hence the reaction will vary with fixa- 

 tion and other preliminary treatments. Fresh material, without fixation, gives 

 even more reliable results. 



EARLY BLASTULA 



GASTRULA 



Distribution of -SH proteins 

 (nitroprusside test) at the 

 beginning (a) and end (b) of 

 oogenesis. (Redrawn from 

 Brachet, 1944) . 



The distribution of basophilic granules 

 (dots) and the sulfhydril proteins 

 (dashes) (after Brachet, 1938) . 



Location of the -SH proteins by the nitroprusside test during various stages In 

 the early development of the amphibian embryo (Redrawn from Brachet, 1944) . 



