60 MICROSCOPIC TECHNIQUES 



immediately in 1% nitric acid and dehydrate rapidly in absolute 

 alcohol. 



3. Clear in xylol and mount in balsam. 



Result. A brick-red or rose color develops in the presence of 

 tyrosine or proteins containing tyrosine. 



a-AMINO ACID GROUPS IN PROTEINS 



Less soluble peptides and proteins containing a-amino acids may 

 be demonstrated at their loci in tissue sections by either the alloxan 

 or ninhydrin reactions. A tendency for the color to diffuse in the 

 alloxan reaction indicates that caution should be applied in inter- 

 preting the test, as Giroud (1929) has warned; furthermore the 

 specificity is not great enough to exclude the need for confirmatory 

 tests (Romieu, 1925). Hence only the ninhydrin reaction of Berg 

 ( 1926) will be described. A positive reaction is obtained with many 

 amines, aldehydes, and ammonium compounds as well as with the 

 amino acids, but the solubility of these compounds enables their 

 easy removal as a rule. 



Berg Ninhydrin Test for a-Aniino Acid Groups 



SPECIAL REAGENTS 



0.2% Ninhijdrin. 



PROCEDURE 



1. Fix tissue in 10% formalin. 



2. Wash in water and prepare frozen sections. 



3. Boil sections in 2 ml. of the ninhydrin soln. for 1 min. 



4. Wash in water and mount in glycerin or glycerin jelly. 



Result. a-Amino acid groups give rise to an intense blue or violet 

 color; this should be observed the same day as it fades rapidly. 



note: Sena and Quieroz Lopes (1945) emploj^ed a mixture of equal vol. 

 of 0.4% ninlij'drin in distilled water and phosphate buffer of pH 6.98 (6 ml. 

 M/15 secondary sodium phosphate — 1L1876 g. Na2HP04.2Hi.O per liter — 

 and 4 ml. M lib primary potassium phosphate — 9.078 g. KHsPO* per liter). 

 They heat the sections in the liquid in a watch glass placed over a boiling 

 water bath. For cementing of the preparations they employ the mixture of 

 Romeis, which is 80 g. colophonium and 20 g. carefully heated lanolin. 



