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TYROSINE. 153
Naturally occurring tyrosine and that obtained by the cleavage of
protein substances by acids or enzymes, is generally /-tyrosine, while
that obtained by decomposition with baryta-water or prepared syn-
thetically is inactive, v. Lippmann l
has obtained d-tyrosine from
beet-sprouts. The statements as to specific rotation of tyrosine are
somewhat variable. For tyrosine from proteins E. Fischer has found
a rotation of (a) D =— 12.56 to 13.2° for the hydrochloric acid solution,
while Schulze and Winterstein 2
obtained higher results using tyrosine
from plants, namely, (a) D =— 16.2°.
Tyrosine in a very impure state occurs in the form of balls similar
to leucine. The purified tyrosine, on the contrary, appears as colorless,
silky, fine needles which are often grouped into tufts or balls. It is diffi-
cultly soluble in water, being dissolved by 2454 parts of water at 20° C,
and 154 parts boiling water, separating, however, as tufts of needles on
cooling. It dissolves more easily in the presence of alkalies, ammonia,
or a mineral acid. It is difficultly soluble in acetic acid. Crystals of
tyrosine separate from an ammoniacal solution on the spontaneous
evaporation of the ammonia. One hundred parts glacial acetic acid
dissolve on boiling only 0.18 part tyrosine, and by this means, especially
on adding an equal volume of alcohol before boiling, the leucine can be
quantitatively separated from the tyrosine (Habermann and Ehren-
feld 3
) . The Z-tyrosine-ethyl-ester crystallizes in colorless prisms which
melt at 108-109° C. The naphthylisocyanate-Z-tyrosine melts at 205-
206°. Tyrosine can be oxidized with the formation of dark-colored
products by various plant as well as animal oxidases, so-called tyro-
sinases (see Chapters XV and XVI). In alcoholic fermentation of sugar
the tyrosine present at the same time is transformed according to F.
Ehrlich 4
into tyrosol (p-oxyphenylethyl alcohol), C8H10O2. Tyrosin is
identified by its crystalline form and by the following reactions:
Piria’s Test. Tyrosine is dissolved in concentrated sulphuric acid
by the aid of heat, by which tyrosine-sulphuric acid is formed; it is
allowed to cool, diluted with water, neutralized by BaCC>3, and filtered.
On the addition of a solution of ferric chloride the filtrate gives a beautiful
violet color. This reaction is disturbed by the presence of free mineral
acids and by the addition of too much ferric chloride.
Hofmann’s Test. If some water is poured on a small quantity of
tyrosine in a test-tube and a few drops of Millon’s reagent added and
1
Ber. d. d. chem. Gesellsch., 17.
2
See Hoppe-Seyler-Thierfelder,-Handb. d. physiol. u. pathol. chem. Analyse, 8.
Aufl., 1909. Also E. Fischer, Ber. d. d. chem. Gesellsch., 32; Schulze aud Winter-
stein, Zeitschr. f. physiol. Chem., 45.
3
Zeitschr. f. physiol. Chem., 37.
4
Ber. d. d. chem. Gesellsch., 44.
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