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180 THE PROTEIN SUBSTANCES.
tared 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 l
and which is the pen-
toside of inosinic acid and is a combination of hypoxanthine with pentose
(f?-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 Schtjlze 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 1
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 cytosine 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.
’
E. Bchulze and Bosshard, Zeitschr. f. physiol. Chem., 10; with Trier, ibid., 70.
• Bioch. Zeitschr., 28.
4
Mandel and Dunham, Journ. of biol. Chem., 11; Levene and Jacobs, ibid., 12.
5
Ber. d. d. chem. Gesellseh., 45.
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