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190 THE PROTEIN SUBSTANCES.
to this mixture, at first a dark green and then quickly a brownish halo
forms around the xanthine grains and finally disappears (Hoppe-Seyler).
If xanthine is warmed in a small vessel on the water-bath with chlorine-
water and a trace of nit.’ic pcid, and evaporated to dryness, and the
residue is then exposed under a bell-jar to the vapors of ammonia, a
red or purple-violet color is produced (Weidel’s reaction). E. Fischer x
has modified Weidel’s reaction in the following way: He boils the xan-
thine in a test-tube with chlorine-water or with hydrochloric acid and a
little potassium chlorate, then evaporates the liquid carefully, and moistens
the dry residue with ammonia.
HN—CO
! I
Guanine, C5H5N50,=H2N.C C—NH\ (2-amino-6-oxypurine)
.
II II
>CH
N—C— W
Guanine is found in all organs rich in cells. It is further found in the
muscles (in very small amounts), in the scales and in the air-bladder of
certain fishes, as iridescent crystals of guanine-lime; in the retinal epithe-
lium of fishes, in guano, and in the excrement of spiders it is found as
chief constituent. It also occurs in human and pig urine. Under patholog-
ical conditions it has been found in leucsemic blood, and in the muscles,
ligaments, and articulations of pigs with guanine-gout.
Guanine is a colorless, ordinarily amorphous powder, which may be
obtained as small crystals by allowing its solution, in concentrated
ammonia, to evaporate spontaneously. According to Horbaczewski it may
under certain conditions appear in crystals similar to creatinine-zinc chlor-
ide. It is insoluble in water, alcohol, and ether. It is rather easily dissolved
by mineral acids and readily by alkalies, but it dissolves with great
difficulty in ammonia. According to Wulff 2
100 cc. of cold ammonia
solution containing 1, 3, or 5 per cent NH3 dissolve 9, 15, or 19 milli-
grams of guanine respectively. The solubility is relatively increased
in hot ammonia solution. The hydrochloride readily crystallizes, and
has been recommended by Kossel 3 for the microscopical detection of
guanine, on account of its behavior toward polarized light. The sul-
phate contains 2 molecules of water of crystallization, which is completely
expelled on heating to 120° C., and this fact, as well as the fact that
guanine yields guanidine on decomposition with chlorine-water, differ-
entiates it from 6-amino-2-oxypurine, which is considered as an oxida-
tion product of adenine and possibly occurs as a chemical metabolic
1 Ber (1 deutsch. chem. Gesellsch., 30, 2236.
2
Zeitschr f. physiol. Chem., 17.
3
Ueber die chem. Zusammensetz. der Zelle, Verh. d. physiol. Gesellsch. zu Berlin
1890-91, Nop. 5 and 6.
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