Full resolution (JPEG) - On this page / på denna sida - II. The Protein Substances - I. Simple Proteins - A. True Albuminous Bodies - Color Reactions for Proteid Bodies
<< prev. page << föreg. sida << >> nästa sida >> next page >>
Below is the raw OCR text
from the above scanned image.
Do you see an error? Proofread the page now!
Här nedan syns maskintolkade texten från faksimilbilden ovan.
Ser du något fel? Korrekturläs sidan nu!
This page has never been proofread. / Denna sida har aldrig korrekturlästs.
PROTEIN REACTIONS. 101
with sodium nitroprusside and ammonia. This reaction is not given by
all proteins and is due to the cystine groups. 9, Abderhalden and
Schmidt’s reaction with triketohydrindenhydrate which gives a blue
coloration on boiling. The triketohydrindenhydrate (also called "Nin-
hydrin ") reacts with all compounds which have an amino group in
the a-position to the carboxyl, is according to Abderhalden and
Hchmidt l
an excellent reagent for the detection of dialyzable amino-
acids and non-biuret giving amino-acid derivatives. They have been
able to detect by this reagent such non-biuret giving substances in the
dialysate on the dialysis of different animal fluids. They have also
determined the delicacy of this reagent with different amino-acids.
The biuret reaction is not only given by protein substances, but also by many
other bodies. According to H. Schiff 2
this reaction occurs with those bodies
containing amino groups, COXH2 , CSNH«, C(NH)XH2 or also CHaNHj, united
either directly by their carbon atoms or by means of a third carbon or nitrogen
atom. As examples of such bodies we can mention several diamines or amino-
amides, such as oximide, biuret, glycinamide, a- and /3-aminobutyramide, aspartic-
acid amide, etc., although we are not certain as to the conditions necessary for the
bringing about of this reaction. The biuret reaction alone is therefore no proof
as to the protein nature of a substance—for example, urobilin gives a very similar
color reaction—and a protein substance can still retain its protein nature, as by
the action of nitrous acid or by a splitting off of ammonia, although it does not
give the biuret reaction.
The delicacy of the various reagents differs for the different proteids,
and on this account it is impossible to give the degree of delicacy for
each reaction for all proteids. Of the precipitation reactions. Heller’s
test (if we eliminate the peptones and certain proteoses) is recommended
in the first place for its delicacy, though it is not the most delicate reac-
tion, and because it can be performed so easily. Among the precipita-
tion reactions, that with basic lead acetate (when carefully and exactly
executed) and with alcohol and the reactions given under 6, are the most
delicate. The color reactions 1 to 4 show great delicacy in the order in
which they are given.3
No proteid reaction is in itself characteristic, and, therefore, in testing
for proteids one reaction is not sufficient, but a number of precipitation
and color reactions must be employed.
For the quantitative estimation of coagulable proteids the determina-
tion by boiling with acetic acid can be performed with advantage, for
by operating carefully, it gives exact results. Treat the proteid solution
with a 1-2 per cent common-salt solution, or if the solution contains
large amounts of proteid dilute with the proper quantity of the above
salt solution, and then carefully neutralize with acetic acid. Now deter-
1
Zeitschr. f. physiol. Chem., 72 and 85.
2
Ber. d. d. chem. Gesellsch., 29 and 30.
3
In regard to the precipitation and color reactions of proteids with aniline dyes
zee Heidenhain, Pfluger’s Arch., 90, 96.
<< prev. page << föreg. sida << >> nästa sida >> next page >>
