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140 THE PROTEIN SUBSTANCES.
the benzoic acid is removed, the filtrate concentrated, the remaining
benzoic acid removed by extracting with ether, the sulphuric acid pre-
cipitated by BaCOs, and the filtrate evaporated to the point of crys-
tallization. (In regard to its preparation from protein substances see
below.)
CH3
d-Alanine(a-aminopropionic acid), C3H7N02 = CH(NH2 ). The d-alanine
COOH
is obtained in relatively small amounts from the true proteids, but in
larger quantities from the albuminoids, especially from fibroin, spider-
silk and elastin.
d-alanine has been prepared from Z-serine by E. Fischer and K.
Raske,1
and Fischer has also obtained it from racemic alanine by split-
ting the benzoyl combination, or from Z-alanine by splitting with yeast
by Walden’s reversion.
Alanine generally crystallizes in needles or oblique rhombic columns.
It is very readily soluble in water, having a sweetish taste, and dissolves
cupric hydroxide on boiling, producing a deep blue solution of a crystalliza-
ble copper salt. Alanine is insoluble in absolute alcohol. The rota-
tion of alanine at 20° C. in aqueous solution is (a) D =+2.7° and for a
solution in hydrochloric acid (9-10 per cent solution) is (ct) D = +10.3°.
The /3-naphthalene-sulpho-d-alanine melts, when dry, at about 123°
and sinters at 117° C. The phenylisocyanate melts at 168° and the
a-naphthylisocyanate alanine melts at 198°. On putrefaction alanine
yields propionic acid.
CH3CH3
V
ClT
d-Valine (a-amino-valeric acid), C5HnN02 = ^TT , ATTT N , u
n CH(NH2), has been
COOH
detected several times among the cleavage products of protein sub-
stances, although only in small quantities. Kossel and Dakin obtained
4.3 per cent valine from salmine, and E. Fischer and Dorpinghaus 2
5.7 per cent from horn substance. The largest quantity has been obtained
from casein and edestin, namely, 7.20 and 5.6 per cent respectively.
Because of the difficulty in separating valine from the two leucines 3
the figures given are somewhat uncertain. The acid isolated by H.
and E. Salkowski 4
from putrefying proteid or gelatin seems to have
been 5-amino-n-valeric acid.
1
Ber. d. d. chem. Gesellsch., 40.
2
Kossel and Dakin, Zeitschr. f. physiol. Chem., 41; Fischer and Dorpinghaus,
i\nd., .’{<>.
-<•<• Levene and v. Slyke, Journ. of Biol. Chem., 6.
4
Ber. d. d. chem. Gesellsch., 16 and 31.
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