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150 THE PROTEIN SUBSTANCES.
compound passes to the anhydride, which is a hydantoin melting at
119° C. By the action of potassium cyanide Mauthner l
obtained
a-amino-jS-suphocyanpropionic acid, CH2 (SCN).CH(NH2 )COOH.
Stone-cystine, according to Neuberg and Mayer, differs in many respects
from the ordinary cystine, among which the following may be mentioned: The
optically active stone-cystine crystallizes in needles, the specific rotation is
(a)D=-206°; it melts’ at 190-192° with marked swelling up. The benzoyl
compound melts at 157-159°; the phenylcyanate compound melts at 170-172°,
and it is not changed on boiling with hydrochloric acid,
In the detection and identification of cystine we make use of the
crystalline form, the behavior on heating on platinum-foil, and the sul-
phur reaction after boiling with alkali. As to its preparation from protein
substances see K. Morner and Folin 2
. In regard to the detection
of cystine in the urine see Chapter XIV.
CH2 .SH
Cysteine (a-amino-/3-thiolactic acid), C3H7 NS02=CH(NH2 ), is formed from
COOH
cystine by reduction with tin and hydrochloric acid. It is also produced in the
cleavage of protein substances not as Embden believes as a primary formation
but according to Morner and Patten 3
as a secondary formation. Cysteine
can be easily converted into cystine by oxidation.
According to V. Arnold4
cysteine occurs as a constituent of the press-juice
or extracts of various animal organs. He has found it especially in the hair and
he considers it as a primary cell constituent.
Toward alkalies and lead acetate it acts like cystine. With sodium nitro-
prusside and alkali it gives a deep purple-red coloration; with ferric chloride
the solution gives an indigo-blue coloration which quickly disappears.
CH3
Thiolactic acid (a-thiolactic acid), C3 K6S02 =CH(SH), has been found once
COOH
as a cleavage product of ox-horn by Baumann and Sitter. Morner, Fried-
mann and Baer obtained it from cystine. It has been shown by Friedmann
that this acid is a regular cleavage product of keratin substances, and that it
can also be obtained from the proteins. Frankel 5
obtained the acid from
haemoglobin. The pyroracemic acid obtained by Morner as a decomposition
product from several protein substances originates, according to Morner, only
in part from the cystine.
Taurine (aminoethylsulphonic acid), C2H7NS03 = Act
-
(SO Vym ’
^as
not been obtained as a cleavage product of protein substances; still its
1
Zeitschr. f. physiol. Chem., 78.
2
Morner, Zeitschr. f. physiol. Chem., 34; Folin, Journ. of Biol. Chem., 8.
3
See foot-note 2, rage 80.
Zeitschr. f. physiol. Chem., 70.
5
Morner, Zeitschr. f. physiol. Chem., 42; Suter, Zeitschr. f. physiol. Chem., 20;
Friedmann, Hofmeister’s Beitrage, 3; with Baer, ibid., 8; Frankel, Sitzungsber. d.
Wien. Akad., 112, II, b, 1903.
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