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132 THE PROTEIN SUBSTANCES.
The older view that in peptic digestion only proteoses and peptones,
but no simpler cleavage products, are formed, has been shown not to be
true. The works of Zunz, Pfaundler, Salaskin, Lawrow, Lang-
stein,1
and others have shown that by very lengthy digestion amino-
acids may in part be formed and also other products such as oxyphenyl-
ethylamine, tetra- and pentamethylenediamine. The biuret reaction
does not disappear and the above mentioned products seem to be formed
only under special conditions. In ordinary, not too lengthy pepsin,
digestion, it is generally admitted that no amino acids are formed but
only proteoses and peptones.
In connection with the above-mentioned experimental results it must be
remarked that not all the products found, for example, the oxyphenylethylamine
and the diamines, are produced by the action of pepsin, but rather by the action of
other enzymes. In certain cases, undoubtedly, impure pepsin was used, or indeed
autodigestion of the stomach was carried on, and the action of other enzymes
was not excluded. In other cases the digestion with pepsin and considerable
acid (even 1 per cent H2S04 ) was continued for a very long time, indeed for an
entire year, without controlling the influence of the acid alone upon the proteoses.
Kuhne’s view that in tryptic digestion (pancreatic digestion) a
peptone, so-called antipeptone, always remains which cannot be further
split is not strictly true. By sufficiently long autodigestion of the pan-
creas, Kutscher 2
was able to obtain, as final products, a mixture of
digestion products which failed to respond to the biuret test, and the same
results have been obtained by others. An antipeptone in the old sense,
i.e., a digestion product which is resistant to tryptic digestion but which
still gives the biuret test, is without question not always obtained as end
product in trypsin digestion. On the contrary as Fischer and Abder-
halden 3
have shown, polypeptide-like bodies are produced in tryp-
tic digestion (and the same is probably true also for peptic digestion)
which do not give the biuret test, i.e., " abiuret " products, and which
are resistant to further tryptic digestion but yield amino-acids on
hydrolysis with acids. This behavior stands in close relation to the
observation that in tryptic digestion certain amino-acids, such for example,
as tyrosine, tryptophane and leucine are split off earlier and more readily
than the others of the protein molecule.
Antipeptone, which is only attacked with great difficulty by trypsin
has in fact been isolated by Siegfried (see below) and although the
’
Zunz, Zeitschr. f. physiol. Chem., 28, and Hofmeister’s Beitrage, 2; Pfaundler,
Zeitschr. f. physiol. Chem., 30; Salaskin, ibid., 32; Salaskin and Kowalewsky, ibid.,
38; Lawrow, ibid., 33; Langstein, Hofmeister’s Beitrage, 1 and 2.
2
Zeitschr. f. physiol. Chem., 25, 26, 28, and Die Endprodukte der Trypsinver-
dauung, Habilitationsscbxift Strassburg, 1899.
3
Zeitschr. f. physiol. Chem., 39.
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