252 Biological Chemistry. 



On complete hydrolysis this nucleotide undergoes scission 

 into phosphoric acid, thymine, and laevulinic acid, 

 CH 8 'CO-CH 2 -CH 2 -CO'OH, a substance which is formed 

 along with formic acid when a hexose is treated with 

 mineral acids 



C 6 H 12 6 = C 5 H 8 3 + CH 2 0^ + H 2 



It is not yet certain how many nucleic acids exist, but 

 there are indications that the nucleic acids obtained from 

 different animal tissues are identical. On the other hand, 

 they appear to differ from the plant nucleic acids, such as 

 the yeast nucleic acid, and the so-called triticonucleic acid 

 of the wheat embryo, in that on hydrolysis with acids the 

 latter yield, not Isevulinic acid like the thymus nucleic acid, 

 but furfurol. These results indicate that the carbohydrate 

 in the plant nucleic acids is a pentose (see p. 210), and not 

 a hexose. By hydrolyzing yeast nucleic acid with water 

 in neutral solution at 175, Levene and Jacobs succeeded 

 in isolating four nucleosides, namely, guanosine, adenosine, 

 cytidine, and uridine, each of which on further hydrolysis 

 yields a pentose and guanidine, adenine, cytosine, and 

 uracil respectively. The pentose obtained was found to 

 be different from all the other hitherto known pentoses, 

 and to have the stereochemical configuration of a sugar, 

 to which the name cZ-ribose * had been assigned. Now 

 the above nucleosides, on condensation with phosphoric 

 acid, should yield the corresponding nucleotides. It 

 has been assumed that yeast nucleic acid is formed by 

 the condensation of four such nucleotides, and has the- 

 formula 



* The enantiomorphous Z-ribpse was known before this time, and had been 

 prepared by Fischer and Piloty in 1891. 



