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166 THE PROTEIN SUBSTANCES.
or spherical aggregations. It has a faint bitter taste, gives a crystalline hydro-
chloride which is slightly soluble in strong hydrochloric acid, and gives a crys-
talline copper salt.
After describing the different amino-acids it remains for us to call
attention to certain general reactions of the amino-acids.
By the action of formaldehyde the amino groups are changed into
methylene groups according to the scheme:
R.CH.NH2 R.CH.N : CH2
+HCOH = I
+H20.
COOH COOH
The amino-acids behave like neutral bodies while the methylene
combinations are acids and on this behavior is based Sorensen’s 1
formoltitration which serves for the estimation of amino-acids in the
urine (Chapter XIV) as well as to follow the progress of proteolysis.
As the proteolysis progresses and imide bindings are loosened a large
number of atomic complexes with free NH2 and COOH groups are set
free. If now the NH2 groups are fixed as methylene groups by the addi-
tion of formol, the complex behaves like acids and the number of their
. . . N
COOH groups can be determined by titration with — barium or sodium
5
hydroxide solution, using phenolphthalein or thymolphthalein as in-
dicator. With the presumption that for every COOH group set free
there existed a free NH2 group the extent of the proteolysis can also
be expressed in milligrams N by multiplying the number of cubic centi-
N
meters — alkali used by 2.8.
5
Siegfried has found that amino-acids in the presence of alkali or
alkaline earths de-ionize carbon dioxide and form salts of the type of
the carbamino salts, Siegfried’s " carbamino-reaction." For example
glycocoll in the presence of lime yields with carbon dioxide, calcium
carbamino-acetic acid, CH2.NH.COO
I I •
COO Ca
If the nitrogen is determined and at the same time the combined carbon
dioxide estimated by means of the calcium carbonate split off on boil-
CO
ing the filtered solution, then the quotient —— gives the number of N
atoms for every molecule CO2 taken up. This quotient is equal to 1
for glycocoll and the aliphatic amino-acids because these go over quan-
1
Sorensen, Bioch. Zeitschr., 7; with Jessen Hansen, ibid., 7; with V. Henriques,
Zeitschr. f. physiol. Chem., 63 and 64; Henriques and Gjaldbak, Ibid., 67 and 75.
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