128 PHYSIOLOGICAL CHEMISTRY 



All of the physiologically important purine bodies are precipitated 

 by ammoniacal silver nitrate solution in the cold and by copper sul- 

 phate and sodium bisulphite in boiling solutions. Some of them are 

 readily identified by their crystalline forms or the crystalline forms of 

 certain of their salts. Uric acid differs from the other purines in being 

 insoluble in dilute sulphuric acid. The purine bodies may be distin- 

 guished to a certain extent also by the reactions which they give when 

 their solutions are evaporated with nitric acid and the residue treated 

 with ammonia. Uric acid gives the characteristic formation of the 

 purple murexide (ammonium purpurate) . Potassium hydroxide changes 

 this to a bluish-violet color which disappears on heating. Xanthine 

 and guanine form yellow compounds with nitric acid which turn 

 purple or violet on treating with potassium hydroxide. The color in 

 this case is not lost by heating. Adenine and hypoxanthine do not 

 give a color reaction with nitric acid. 



The Pyrimidine Bases. The pyrimidine bases entering into the 

 composition of nucleic acid are thymine, cytosine and uracil. Cytosine 

 is found in both types of nucleic acid, while thymine is found only 

 in animal nucleic acid and uracil only in plant nucleic acid. They 

 possess the following formulas. 



NH C= O NH C N= -C NH 2 



O=C CH O C C CH 3 O=C CH 



I II II II 



NH CH NH CH NH CH 



Uracil Thymine Cytosine 



2-6-dioxypyrimidine 5-methyl- 6-amino- 



2-6-dioxypyrimidine 2-dioxypyrimidine 



With regard to the fate of pyrimidine bases in metabolism very 

 little is known. When the bases as such are fed they reappear un- 

 changed in the urine. 1 If nucleic acid is fed this does not occur which 

 indicates that the pyrimidine bases may undergo certain alterations 

 in the animal body while still existing in combination. 



EXPERIMENTS 



i. Preparation of Nucleoprotein from Yeast. 2 Place two small cakes of ordi- 

 nary compressed yeast in a mortar. Sprinkle a small horn-spoonful of sand over 

 the yeast, add 5 c.c. of ether and 10 c.c. of water and thoroughly triturate the 

 mixture, grinding vigorously. The ether kills the yeast, in which condition the 

 comminution of the cells with sand is more thoroughly affected. Occasionally 

 during the trituration process add i or 2 c.c. of water until the mixture is 

 comparatively fluid. The whole process of maceration can be completed in five 



1 Mendel and Myers: Am. J. Physiol., 26, 77, 1910. 



2 All experiments on nucleoprotein of yeast have been taken from Laboratory Notes of 

 Professor W. J. Gies, of College of Physicians and Surgeons, New York. 



