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ENZYMES. 49
The aqueous solutions can be kept at low temperatures for a long time
after the addition of toluene or chloroform.
In all these cases the enzymes are obtained strongly contaminated
with other bodies, especially by proteins. Only in exceptional cases is
it possible to free the enzyme solution from protein so that the solution
does not give the ordinary protein reactions. This is true for the solu-
tion of saccharase obtained from yeast by treatment with water; if
this is shaken with kaolin the protein is adsorbed by the kaolin while the
solution contains the enzymes.1
No enzyme has thus far been obtained in a perfectly pure form,
and the chemical constitution as well as structure is therefore unknown.
The enzymes probably belong to the colloids; if they themselves are not
colloids, they occur at least with colloids, from which they may be sepa-
rated only with difficulty, if at all. The enzymes are characterized by
the fact that they are readily taken up by finely divided substances
(inorganic precipitates, carbon, kaolin, infusorial earth and other col-
loids such as alumina, iron hydroxide, proteins 2
) . This process may
act selectively, as from a solution certain enzymes can be taken up and
others not at all, or only to a slight extent (Hedin,3
Michaelis and
Ehrenreich 4
). The adsorption process is more or less irreversible
and differs in this from the adsorption of crystalloid substances. Still
the trypsin and rennin adsorbed by charcoal can be to a slight extent
expelled from the charcoal by means of other adsorbable substances such
as casein and albumin (Hedin).5
Rennin taken up by charcoal can to
a very slight extent be set free by the addition of glucose (Hedin) and
saccharase adsorbed by charcoal can be set free by cane-sugar (Eriks-
son).6
As we will learn below, the adsorbed enzyme is inactive. The
so-called shaking inactivation of enzymes or the loss in activity of enzymes,
which occurs on shaking their solution seems to be due to an adsorp-
tion of the enzyme when it is either taken up by the precipitate
formed on shaking (Abderhalden and Guggenheim) or is concentrated
at the surface between the solution and the froth (S. and S. Schmidt-
Nielsen).7
These latter found the inactivation of rennin by shaking
was regained if the froth was allowed to subside.
All enzymes lose their specific action on sufficiently heating their
1
Michaelis, Bioch. Zeitschr., 7, 488 (1907).
2
Dauwe, Hofmeister’s Beitrage, 6, 426 (1905).
3
Bioch. Journ., 2, 112 (1907).
« Bioch. Zeitschr., 10, 283 (1908).
6
Bioch. Journ., 2, 81 (1906); Zeitschr. f. physiol. Chem., 63, 143 (1909).
6
Hedin, ibid., 63, 143 (1909); Ericksson, ibid., 72, 313 (1911).
7
Abderhalden and Guggenheim, Zeitschr. f. physiol. Chem., 54, 352 (1907); S. and
S. Schmidt-Nielsen, ibid., 68, 317 (1910) which also contains the literature.
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