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NUCLEIC ACIDS. 181
The simple nucleic acids are ester-like combinations between phosphoric
acid and a purine base-pentoside.
The complex nuclei acids arc complex molecules each composed of
four simple nucleic acids (nucleotides). In regard to the complex nucleic
acids we differentiate between two groups.
The acids of the thymonucleic acid group are, according to Steudel,
tetrabasic phosphoric acid ester which corresponding to each phosphorus
atom, contains a hexose group and one of the four bases, guanine,
adenine, cystosinc and thymine. From the name of this group we infer
that these acids contain thymine.
The plant nucleic acid group differs from the preceding by the follow-
ing. They do not contain any thymine but uracil instead. They do not
contain any hexose but do contain pentose. In the acids of this group
for each atom of phosphor we have 1 mol. pentose and on each the
purine and pyrimidine bases are combined.
It must be remarked that the complex nucleic acids have not been
prepared from isolated component proteins but generally from organs,
namely perhaps from a mixture of different nucleoproteins and that for
this reason we do not know whether these acids are chemical individuals
or only a mixture of closely related simple nucleic acids. On the other
hand it is also possible that the simple nucleic acids originate from more
complex nucleic acid by cleavage because such cleavages are in fact
known. Such an assumption does not apply at least for the guanylic
acid from the pancreas as it is obtained from a compound protein with
only one base, namely guanine.
All nucleic acids are amorphous, white, and have an acid reaction.
They are readily soluble in ammoniacal or alkaline water. They also
dissolve in concentrated acetic acid and form insoluble salts with copper
chloride and salts of the heavy metals, and as a rule insoluble basic
salts with the alkaline earths. Their solubility in water is very different.
Inosinic acid, for example, is very readily soluble in cold water while
tf-guanylic acid is soluble with difficulty. The complex nucleic acids
are also soluble with difficulty in cold water. The solution of their
alkali combination is not as a rule precipitated by acetic acid but is
precipitated by a slight excess of hydrochloric acid, especially in the pres-
ence of alcohol. The nucleic acids soluble in dilute acids give in such
solution a precipitate with proteins, which are considered as nucleins. All
nucleic acids are insoluble in alcohol and ether. They do not give either
the biuret test or Millon’s reaction. The nucleic acids are optically
active and, with the exception of inosinic acid (Gamgee and Jones)
and of guanylic acid (Levene and Jacobs l
), are dextro-rotatory.
1
Gamgee and Jones, Proc. Roy. Soc, 72; Levene and Jacobs, Journ. of biol.
Chem., 12.
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