94 



THE CHEMICAL COMPOSITION OF THE BODY 



Adenine and guanine may be converted into hypoxanthine and xanthine, 

 respectively, when added to extracts of tissues, such as the liver and the thymus, 

 spleen and pancreatic glands. The "deamidization" is brought about by 

 specific enzymes or non-living ferments which have been termed adenase and 

 guanase. On slight oxidation, hypoxanthine is converted into xanthine, and 

 the latter into uric acid. This change can also be brought about in the body 

 by oxidizing enzymes. The relation of the purine bases to uric acid is indicated 

 in the following scheme: 



Adenine. 



(6-amino purine.) 

 N = C-NH 2 



+ H 2 



HC C-NH 



-NH 3 



Hypoxanthine. 

 (6-oxypurine.) 

 HN-C=O 



HC C-NH 



J.L 



HN-C=0 



-c-/ 



CH 



on oxi- 



dation 



HN-C=0 



HN-C=0 



H 2 N-C C- 



+ H 2 



NH 



I I > 

 N-C-N 



-NH 3 



= C 



Guanine. 

 (2-amino 6-oxypurine.) 



on oxidation 

 :-NH O 



>CH 

 HN-C-N 



Xanthine. 

 ( 2-6di-oxypurine.) 



-NH 



>C = 

 HN-C-NH 



Uric acid. 

 ( 2-6-8-trioxy purine.) 



Glycoproteins. The glycoproteins are to be considered as compounds 

 of protein and considerable quantities of a carbohydrate complex. The car- 

 bohydrate group can be split from the protein by boiling with mineral acids or 

 by the action of alkalies. The group of glycoproteins includes a number of 

 proteins, of which the mucines and mucoids are the most important. 



Mucines are very widely distributed. They give the mucilaginous 

 character to many secretions and are formed and discharged through the 

 respiratory, digestive, and other tracts, partly by mucous cells and in part by 

 the mucous glands, especially by the submaxillary and sublingual sali- 

 vary glands, and in the bile passages. On hydrolysis the mucines are split, 

 the carbohydrate moiety yielding glucose amine or galactose amine. 



Mucoids occur in the connecting tissues along with the albuminoids. 

 They are found especially in the tendon, bone, and cartilage. They are 

 combinations of protein and a carbohydrate containing ethereal sulphuric 

 acid known as chondroitin sulphuric acid. On cleavage, besides the products 

 formed from the protein, they yield sulphates and a reducing substance. 



Phosphoproteins. The phosphoproteins, sometimes called nucleo- 

 albumins, are compounds of the protein molecule with some as yet unde- 

 fined phosphorus-containing substance other than a nucleic acid or lecithin. 

 While the phosphorus content of these substances is quite similar to that 



