DECOMPOSITION-PRODUCTS OF THE NUCLEIC ACIDS 177 



The purine bases are all precipitable from acid solutions by phos- 

 photungstic acid or from ammoniacal solutions by silver nitrate. 

 Guanine is insoluble in water, alcohol or ether, but readily dissolves in 

 dilute acids or alkalies (with the exception of ammonia). It does 

 not give Weidel's reaction, but with nitric acid it yields, on evaporation, 

 a yellow residue w T hich turns bluish- violet on heating with sodium 

 hydroxide. With chlorine water guanine decomposes, yielding Guani- 

 dine, Parabanic Acid and carbon dioxide: 



HN CO 



I I 



H 2 NC C NH\ /NH 2 HN CO 



/ I 



+ 3O + H 2 O = HN=C< + OC 



\ I I 



C0 2 



X NH 2 HN CO 



Guanine. Guanidine. Parabanic acid. 



Free guanine is found in the scales and swimming-bladder of fishes. 

 It also occurs occasionally in the form of concretions in the retinal 

 epithelium of fishes and in the joints of pigs suffering from "guanine 

 gout." It forms an important constituent in the excrement of 

 spiders. 



Guanine is hydrolyzed by an enzyme, Guanase which is found in a 

 variety of tissues, particularly those of the pancreas and thymus (but 

 not the Spleen). The products are Xanthine and ammonia: 



HN CO 



H 2 NC C NH\ 



II II \ 



>CH + H 2 O = 



HN 



Guanine. Xanthine. 



Adenine undergoes an analogous change with the production of 

 Hypoxanthine, but the enzyme which brings this about (Adenase) 

 appears to be a different one from that which accomplishes the deamini- 

 zation of guanine, since it occurs in the spleen, from which guanase is 

 absent. Hence when the tissues of the thymus or pancreas are allowed 

 to undergo Autolysis; that is to say, spontaneous hydrolysis by their 

 own enzymes, the purines which are isolated from the mixture are 

 the oxypurines, xanthine and hypoxanthine, instead of the amino- 

 purines, guanine and adenine which result from hydrolysis by acids. 



Adenine is sparingly soluble in cold, but readily soluble in hot water; 

 it is readily soluble in acids and alkalies. Adenine does not give 

 Weidel's reaction. With nitric acid, on evaporation, it gives a nearly 

 12 



