PURINES 93 



Nucleic acids are white, amorphous substances containing 9 to 10 per cent, of 

 phosphorus. According to Levine the composition corresponds to C43H 6 7Ni 6 P 4 Ojo. 

 Nucleic acids give none of the protein reactions. In the sperm they are united with the 

 strongly basic protamines and so are acid in character. They may be precipitated, 

 however, by tannic acid, picric acid, or phosphotungstic acid as are other organic bases. 

 Nucleic acid has been isolated from many different tissues and apparently is a 

 uniform constituent of the nuclei of all cells. The nucleic acids from different animal 

 tissues are apparently identical and similarly the nucleic acids of vegetable origin are 

 identical, though there are marked chemical differences between these two types. 



The structure of plant nucleic acid is the better known of the two. Thanks to the 

 extensive investigations of Levine, and Jones, and their co-workers, plant nucleic acid 

 has been shown to be composed of four different nucleotides. These nucleotides are 

 composed of a purine or pyrimidine base linked to phosphoric acid by carbohydrate 

 groups. In the case of yeast or plant nucleic acid, the carbohydrate is a pentose 

 (d. Ribose). The first of the nucleotides studied was guanylic acid which contains the 

 purine base quanine or 2 ammo- 6 oxypurine. 



O = C NH 

 O H H H H H || 



MM! /NH-C C = NH 

 HO P O C C C C C C 



\N C NH 

 OH H O OH OH 



Guanylic acid. 



The other three nucleotides contain adenine and the pyramidine bases uracil and 

 cytosine respectively. The tentative structure of yeast nucleic acid is probably that of 

 a tetra nucleotide, though the mode of linkage of the different groups is still in doubt. 

 HO\ 



HO/ guanine. 



H0\ 



HO/ cytosine. 



HO\ 



O = PO.C5H 8 O3.C4H 3 N a O 2 

 HO/ uracil. 



HO\ 



0=PO.C6H 8 O 3 C 6 H 4 N 6 

 HO/ adenine. 



The structure of animal nucleic acid is less well known. It contains a hexose instead 

 of a pentose group and thymine in place of uracil. 



Purines. To the purines belong a number of extremely important animal 



and plant substances, including adenine, guanine, hypoxanthine, xanthine, 



and uric acid, and the methyl purines caffeine, theobromine, and theophylline. 



The mother substance of the purines is known as purine, which has the 



following structure: 



iN-C 6 N = CH 



a C C 5 -N\ HC 6-NH 



1 / 8 \CH 



6- N 9 / / un 



N_ C -N 

 Purine ring. Purine. 



