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PEPSIN. 467
the mucous membrane, cannot, according to Hammarsten, either be the
only or the most prominent peptic enzyme of the pyloric part. According
to Glaessner, it also acts in neutral and alkaline reaction and yields
tryptophane among other cleavage products. According to Bergmann l
it is identical with erepsin (see below). Among the enzymes of the
mucosa of the stomach belongs the so-called antipepsin discovered by
Weinland,2
which has a retarding action upon pepsin digestion and,
as some claim, prevents the self-digestion of the mucous membrane.
Pepsin is as difficult to isolate in a pure condition as are other
enzymes. The pepsin prepared by Brucke and Sundberg gave negative
results with most reagents for proteins, and showed nevertheless a
powerful action, which seems to indicate that it was very pure. Schou-
mow-Simanowski, Nencki and Sieber, have designated as the true
enzyme the substance containing chlorine, which they obtain by strongly
cooling the gastric juice. That this precipitate is not a chemical indi-
vidual, and hence cannot be pepsin, follows from the investigations of
Pekelharing. While pepsin, according to Nencki and Sieber, was
rich in phosphorus and contained nucleoprotein, Pekelharing’s pepsin
was free from phosphorus and yielded no nucleoprotein. Friedenthal
and Miyamota 3
have also shown that the pepsin is still active after
the splitting off of the nuclein complex (and also the protein). As pepsin
is readily precipitated with the proteins and combines therewith, it is
difficult to decide whether pepsin is a protein substance or not, and the
question as to its nature is still undecided, just as is the case with other
enzymes. As ordinarily known, pepsin, at least in an impure form, is
soluble in water and glycerin. It is precipitated by alcohol, but is only
slowly destroyed thereby. In aqueous solution its action is quickly
destroyed on heating to boiling. According to Biernacki 4
pepsin
in neutral solutions is destroyed by heating to 55° C. In the dry state
it can be heated to over 100° C. without losing its activity. In the
presence of 2 p. m. HC1 a temperature of 55° C. is not injurious, and the
compound with acid is more resistant than the free pepsin (Grober 5
).
Pepsin in acid solution is destroyed by heating to 65° C. for five minutes.
’Glaessner, Hofmeister’s Beitrage, 1; Klug, Pfluger’s Arch., 92; Reach, Hofmeis-
ter’s Beitrage, 4; Pekelharing, Arch, des scienc, biolog., St. P6tersbourg 11; Pawlow-
Festband, 1904; Bergmann, Skand. Arch. f. Physiol., 18.
2
Zeitschr. f. Biologie, 44.
3
Brucke, Wien. Sitzungsber,. 43; Sundberg, Zeitschr. f. physiol. Chem., 9; Schou-
mow-Simanowski, Arch. f. exp. Path. u. Pharm., 33; Pekelharing, Zeitschr. f. physiol.
Chem., 22 and 35; Xencki and Sieber, ibid., 32; Friedenthal and Miyamota, Centrabl.
f. Physiol., 15, 785.
« Zeithschr. f . Biologie, 28.
6
Arch. f. exp. Path. u. Pharm., 51.
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