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154 THE PROTEIN SUBSTANCES.
then the mixture boiled for some time, the liquid becomes a beautiful
red and then yields a red precipitate.
Deniges’ Test, modified by C. Morner, is performed as follows:
To a few cubic centimeters of a solution consisting of 1 vol. formaline,
45 vols, water, and 55 vols, concentrated sulphuric acid add a little
tyrosine in substance or in solution and heat to boiling. A beautiful
permanent green coloration is obtained.
Folin and Denis’s test. The reagent consists of a solution containing
10 per cent sodium tungstate, 2 per cent phosphomolybdic acid and
10 per cent phosphoric acid. In performing the test mix 1-2 cc. of the
reagent with an equal volume of the tyrosine solution and then add 3-10
cc. saturated sodium carbonate solution when a beautiful blue color
results. Its delicacy is 1:1000000. The reagent can also be used for the
colorimetric quantitative estimation of tyrosine in proteins. According
to Abderhalden and Fuchs and to Abderhalden 1
the reagent suggested
by Folin and Denis for tyrosine also gives a blue coloration with trypto-
phane, oxytryptophane and Z-oxyproline and the value of this reagent for
quantitative tyrosine determinations requires further testing.
H2C—CH2
I I
/-Proline (a-pyrolidine carboxylic acid), C5 H9N02 = H2 C CH.COOH,
NH
was first obtained by E. Fischer and then by Fischer and collabora-
tors from several proteins as a primary cleavage product (Abder-
halden and Kautzsch 2
). The proline here obtained was generally
the laevo-rotatory modification. The largest quantity of proline was
secured from the vegetable proteins hordein and gliadin, namely, 13.7
per cent and 13.2 per cent, and also from gelatin, 7.7 per cent (see table
pages 106, 107, 115 and 125). Kossel and Darin 3
obtained 11 per cent
from salmine. Proline also occurs in scombrine and clupeine, but not in
sturine, which, according to Kossel, seems to contradict the view as
to the common origin of ornithine and proline.
Sorensen,4
by means of a general method of preparing a-amino-
acids synthetically, has prepared a-amino-5-cxyvaleric acid from phthali-
midemalonic ester and has obtained proline from this by evaporating with
1
Deniges, Compt. rend., 130; C. Th. Morner, Zeitschr. f. physiol. Chem., 37; Folin
and Denis, Journ. of Biol. Chem., 12; Abderhalden and Fuchs, Zeitschr. f. physiol.
Chem., 83 and Abderhalden, ibid., 85.
2
E. Fischer, Zeitschr. f. physiol. (.’hem., 33 and 35. See also footnote 2, p. 86,
and Abderhalden and Kautzsch, Zeitschr. f. physiol. Chem., 78.
1
Zeitschr. f. physiol. Chem., 41.
4
Zeitschr. f. physiol. Chem., 44; with A. C. Anderson, ibid., 56.
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