162 J. BADDILEY 



Ribonuclease digestion, or very mild alkaline hydrolysis of ribonucleic 

 acid, gives the four possible cyclic nucleoside-2', 3 '-hydrogen phosphates, 

 together with other products. ^^^ These are artifacts, cyclic phosphate struc- 

 tures not being present in nucleic acids, but their formation is significant in 

 connection with the structures proposed for ribonucleic acid (see Chapter 

 12). Ribonuclease digestion of ribonucleic acid also yields a number of di- 

 and trinucleotides, some of which contain cyclic phosphate structures.^"- ^^* 



Pyrimidine deoxyribonucleotides are produced by mild acid hydrolysis 

 of deoxyribonucleic acid."^"''** Both 5'-phosphates and 3',5'-diphosphates 

 are obtained. The purine deoxyribonucleotides are very sensitive to acids 

 and cannot be prepared by chemical hydrolysis of the parent nucleic acid. 

 However, these substances are obtained from the nucleic acid by using an 

 intestinal deoxyribonuclease in the presence of sodium arsenate, thereby 

 inhibiting the action of an accompanying nucleotidase.^*^"''** Recent methods 

 for the isolation of deoxyribonucleotides employ ion-exchange resins."*- 



150, 151 



2. Structure of Nucleotides 



As the nucleotides may differ from each other not only in the nature of 

 the pyrimidine and purine bases attached to either of the sugars D-ribose 

 and D-2-deoxyribose, but also in the location of the phosphoric ester link- 

 age, they are best considered individually. 



a. InosineS' -phosphate (muscle inosinic acid) (XXI) 



This nucleotide is a phosphoric ester containing the components hy- 

 poxanthine'^2 and D-ribose.^-* On neutral hydrolysis it gives phosphoric acid 

 and inosine; consequently it is a monophosphate of inosine in which the 



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