180 THE PROTEIN SUBSTANCES. 



tured while the binding between the pentose and purine bases remained 

 intact. In this manner they obtained pentosides, i.e., glucoside-like com- 

 bination between pentose and a purine base. These pentosides have 

 also been called nucleosides and such a nucleoside was the inosine, 

 which was first found by HAISER and WENZEL 1 and which is the pen- 

 toside of inosinic acid and is a combination of hypoxanthine with pentose 

 (d-ribose). The other three nucleosides adenosine, guanosine and xantho- 

 sine have been prepared by LEVENE and JACOBS. 



The nucleosides are crystalline bodies which give crystalline combina- 

 tions. Of special interest is guanosine because it is identical with the base 

 vernine, occurring in the plant kingdom and discovered by SCHULZE 2 

 and because of the identity of the pentose occurring in both has been 

 positively proved. The guanosine has also been found by LEVENE and 

 JACOBS 3 in the pancreas. On acid hydrolysis every nucleoside splits 

 into purine base and pentose. By the action of nitrite and glacial acetic 

 acid the guanosine is transformed into xanthosine and the adenosine 

 into inosine. 



MANDEL and DUNHAM have prepared, from acetone-yeast, a crystalline 

 adenine-hexose compound corresponding to the pentoside but whose 

 relation to the cleavage products of nucleic acids is not known. From 

 thymus nucleic acid LEVENE and JACOBS 4 have later isolated a guanine 

 hexoside. 



The pyrimidine complexes corresponding to the nucleosides also 

 contain (in the plant nucleic acids) pentose, according to LEVENE and 

 LA FORGE 5 but in much firmer bondage. This is the reason why they 

 give only a faint orcin reaction, are much more resistant to enzymes 

 than the purine nucleosides and give off furfurol only very slowly on 

 distilling with hydrochloric acid. Still they contain pentose and pyrimi- 

 dine bases in equimolecular proportions. The pyrimidine complexes are 

 called cytidine and uridine, the first containing cytosirie and the second 

 uracil. Uridine is crystalline; the cytidine has not been obtained in a crys- 

 talline form but it gives several crystalline salts. The uridine is claimed 

 to exist pre-formed in the yeast nucleic acid and not produced secondarily 

 from the cytidine. 



Based upon the investigations carried out by STEUDEL, LEVENE and 

 JACOBS we can for the present represent the structure of the nucleic acids 

 in the following way: 



1 Monatsh. f. Chem., 29. 



2 E. Schulze and Bosshard, Zeitschr. f. physiol. Chem., 10; with Trier, ibid., 70. 



3 Bioch. Zeitschr., 28. 



4 Mandel and Dunham, Journ. of biol. Chem., 11; Levene and Jacobs, ibid., 12. 

 6 Ber. d. d. chem. Gesellsch., 45. 



