NUCLEIC ACIDS 145 



Just as the free amino-puriries (guanine and adenine) are deaminized to 

 the corresponding oxy-purines (xanthine arid hypoxanthine), so also the 

 amino-nucleosides (guanosine and adenosine) form the corresponding oxy- 

 micleosides (xanthosine and inosine). 



These relations are shown in the following diagram. Horizontal ar- 

 rows indicate hydrolysis ; vertical arrows, deaminbjation. 



C 5 H,X 4 ( Nil, I C 3 H A . C.H a X 4 ( XH 2 ) C 5 H 9 4 . C 5 H 2 X 4 ( XH a } C.H,X 4 ( XH 2 ) 



guanine < guanosine adenosine > adenine 



C 3 H 3 X 4 ( OH ) C 5 H 4 . C 5 H,X 4 O ( OH ) C 3 H a O 4 . C 5 H 2 X 4 ( OH ) C 5 H 3 N 4 (OH ) 



xanthine -- xanthosine inosine - > hypoxanthine 



With the pyrimidine nucleosidcs the matter is a little different. Deamini- 

 zation converts the ainino-nucleoside (cytidine) into its corresponding oxy- 

 nueleoside (uridine). 



C 5 H 9 3 . C 4 II 2 X 2 0(XH 2 ) C 4 H 3 



cytidine cytosirie 



4 1 



C.H,0 S .C 4 H,N.O(OH) C 4 H 3 N 2 0(OH) 



uriUine uraeil 



But the two pyrimidine nucleosides are very stable, and are not hydro- 

 lyzed by mineral acid into pentose and free pyrimidine as is the case 

 with the pnrine nucleosides. Of course it is possible that animal ferments 

 are capable of effecting hydrolysis of the pyrimidine nucleosides. 



One m i<>ht therefore suspect that the metabolism of yeast nucleic 

 acid is a play upon hydrolysis, deaminization and oxidation, which will 

 produce various nucleotides, nucleosides and free bases, and if continued 

 far enough must finally end in the formation of uric acid. In Part II 

 it will be shown that such is actually the case. 



ANIMAL NUCLEIC ACID 



The chemistry of thymus nucleic acid is best appreciated by a com- 

 parison of the substance with yeast nucleic acid. When thymus nucleic 

 acid is boiled with dilute sulphuric acid it easily sets free both of the 

 amino-purines (guanine and adenine), with part of its phosphoric acid and 

 part of its carbohydrate. But when thymus nucleic acid is submitted 

 to severe acid hydrolysis (as with 30 per cent sulphuric acid at 150), 

 the two pyrimidine derivatives are set free with the remainder of the car- 

 bohydrate and phosphoric acid. All of these statements are equally true 

 for yeast nucleic acid ; but it must be noted that thymus nucleic acid 

 yields thymine (Kossel and Ncumaii ()(&), (1893, 181)4)) where yeast 

 nucleic acid yields uraeil. 



