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176 THE PROTEIN SUBSTANCES.
in solution. By the action of weak acids and by gastric juice a similar
cleavage takes place, whereby the protein split off goes into solution
while the nucleoprotein rich in phosphorus, so-called nuclein (Miescher,
Hoppe-Seyler *) or true nuclein, remains undissolved. As the nuclein
is probably nothing but a partly modified nucleoprotein poorer in pro-
tein, having a composition varying with the intensity of the cleavage,
it seems unnecessary to give the name nuclein thereto. On the other
hand, the nucleins have other properties than the nucleoproteins, and
as the nucleins bear the same relation to the nucleoproteins that the
pseudonuclein does to the nucleoalbumins, we will here give a short
description of the nucleins as well as the pseud’o- or paranucleins.
Nucleins or true nucleins are formed, as above stated, from nucleo-
proteins in their peptic digestion or by treatment with dilute acids. It
must be remarked that the nucleins are not entirely resistant toward
gastric juice, and also that at least one nucleoprotein, namely, the one
obtained from the pancreas, completely dissolves, leaving no nuclein
residue on treatment with gastric juice (Umber, Milroy2
). The
nucleins are rich in phosphorus, containing in the neighborhood of 5 per
cent. According to Liebermann,3
metaphosphoric acid can be split
off from true nucleins (yeast nuclein). The nucleins are decomposed
into protein and nucleic acid by caustic alkali, and as different nucleic
acids exist, so also there exist different nucleins. As previously stated
proteins may be precipitated in acid solutions by nucleic acids, and in
this way, as shown by Milroy, combinations of nucleic acid and pro-
teins may be prepared which behave quite like true nucleins. All nucleins
yield purine bases (so-called nuclein bases) on boiling with dilute acids.
They act like rather strong acids.
The nucleins are colorless, amorphous and insoluble or only slightly
soluble in water. They are insoluble in alcohol and ether. They are
more or less readily dissolved by dilute alkalies. The nucleins give the
biuret test and Millon’s reaction. They show a great affinity for many
dyes, especially the basic ones, and take these up with avidity from watery
or alcoholic solutions. On burning they yield an acid residue which
is very difficult to incinerate and which contains metaphosphoric acid.
On fusion with saltpeter and soda the nucleins yield alkali phosphates.
To prepare nucleins from cells or tissues, first remove the chief mass
of proteins by artificial digestion with pepsin-hydrochloric acid, lixiviate
the residue with very dilute ammonia, filter, and precipitate Avith hydro-
chloric acid. The precipitate is further digested with gastric juice,
1
Hoppe-Seyler, Med. chem. Unters., 452.
5
["ruber, Zeitsclir. f. klin. Med., 34; Milroy, Zeitschr. f. physiol. Chem., 22.
3
Pfluger’s Arch., 47.
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