Full resolution (JPEG) - On this page / på denna sida - I. General and Physico-chemical - IV. Enzymes
<< 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.
52 GENERAL AND PHYSICO-CHEMICAL.
salicylate. Enzymes made inactive by dialysis can be activated again
by the addition of boiled enzyme or the concentrated dialysate. Harden
and Young l
on filtering yeast-press juice through earthenware filters
impregnated with gelatin, have found different constituents of the zymase
on the filter and in the filtrate. The true enzyme remains on the filter.
This alone is inactive, but becomes active when the other part which
has passed through the filter, and which is dialyzable and resistant to
temperature, is added. This part is consumed during fermentation
and therefore the enzyme becomes inactive. After the addition of, best,
boiled press-juice to this the fermentation begins again (see also Chapter
III). Certain of the just-mentioned substances which are resistant
to heat, whose presence are necessary for the action of certain enzymes,
are ordinarily called co-enzymes. As they are not to be classified with
the enzymes, they are more correctly called activators, as suggested by
Etjler.2
Their action is probably different in different cases, and
differs also from the activating action of the kinases.
Many enzymes are secreted by the cells as such or as proenzymes.
They act outside of the cells in which they were formed, or they act after
having been transformed into the enzyme, and hence are called secre-
tion enzymes or extracellular enzymes. Besides these extracellular
enzymes we also have another group which acts within the cells, hence
are intracellular and therefore are called intracellular enzymes or endo-
enzymes. To this group belongs, beside the yeast zymase, numerous
enzymes such as oxidases and hydrolytic enzymes.
Formation and Secretion of Enzymes. The investigations of Pawlow 3
and his pupils upon the formation and secretion of the enzymes active
in the alimentary tract are very important. According to these investiga-
tions the amount of secretion of the glands and the behavior of the enzymes
contained in the secretion are dependent upon the amount and com-
position of the food taken and in such a manner that the kinds and
amounts of enzymes are appropriate for the digestion of the food-
stuffs (see Chapter VIII). Similar results were also obtained by Wein-
land 4
who found that the pancreas does not normally contain any
lactase but did contain this enzyme after feeding the animal with
milk or milk sugar. This has been substantiated by Bainbridge.5
Analogous experiments have been made with salivary ptyalin by Neil-
^roc. Physiol. Soc, 32 (1904); Proc. Chem. Soc, 21, 189 (1905); Proc. Roy.
Soc, 77 (ser. B), 405 (1906); ibid., 78, 369 (1906). .
2
Zeitschr. f. physiol. Chem., 57, 92 (1908).
3
Arbeit der Verdauungsdriisen, Wiesbaden, 1898, s. 51.
Zeitschr. f. Biol., 38, 607 (1899); 40, 386 (1900).
6
Journ. of Physiol., 31, 98 (1904).
<< prev. page << föreg. sida << >> nästa sida >> next page >>
