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62 GENERAL AND PHYSICO-CHEMICAL.
and d-galactose, and of the ketohexoses only one, d-fructose are fer-
mentable; and then that the synthetically prepared stereoisomeric
glucosides behave differently with the enzymes. Thus of two isomeric
glucosides, one methyl-d-glucoside, the (a) was attacked by yeast and
the other (j3) only by emulsin, while the corresponding methyW-glucosides
were not split by either of these enzymes. The corresponding glucoside
obtained from galactose behaves in a similar manner.1
On the behavior
of amygdalin to various enzymes see page 59. In connection with
these observations Fischer presents the theory that for the action of
an enzyme a certain correspondence in stereometric structure of the
enzyme and substrate must exist; the enzyme must fit the substrate
somewhat like a key fitting a lock.
Then followed similar observations of Darin,2
who found that racemic
mandelic acid ester, on incomplete hydrolysis by liver press-juice, yielded
a strongly dextrorotatory acid, while the ester remaining was levorotatory.
The dextrorotatory ester was more quickly hydrolyzed than the levoro-
tatory ester. Finally, we must mention the investigations of Fischer
and Abderhalden 3
on the cleavage of polypeptides by pancreas
press-juice. From abundant material they concluded that those polypep-
tides which consist entirely of the optical forms of amino-acids occurring
in nature are hydrolyzed and the others not. If in a racemic form besides
a polypeptide consisting of natural amino-acids, another occurs also,
then only the first is hydrolyzed. Besides this, other factors are also
of importance. Thus Z-leucyl-glycine is not hydrolyzed, although both
constituents occur in nature. The size of the molecule seems also to be
of importance, as mono-, di- and triglycyl-glycine are not split, while
tetraglycyl-glycine is. See also Chapter VIII.
Retardation of Enzyme Action. There are several reasons for the
assumption that the hydrolytic enzymes are only active after they have
combined with the substrate. From this it follows that those substances
which prevent the formation of such combination may cause the retarda-
tion of enzyme action. For this reason the enzyme action is retarded
by such substances which adsorb the enzyme (page 49). Hedin 4
has
made experiments on the retarding action of charcoal upon the action
of trypsin upon casein, and the action of rennin upon milk and it was
shown that the retardation was more pronounced if the powder and
enzyme were allowed to act upon each other before the substrate was
added than if this was present from the beginning. This fact indicates
1
Zeitschr. f. physiol. Chem., 26, 60 (1898) (collection of Fischer’s works).
Mourn, of Physiol.’, 30, 253 (1903); 32, 199 (1905).
•Zritechr. f. physiol. Chem.,’ 46, 52 (1905); 61, 264 (1907).
•Bioch. Jpurn., 1, 484; 2, 81 (1906); Zeitschr. f. physiol. Chem., 50, 497 (1907);
60, 143 (1909). See also Jahnson-Blohm, ibid., 82, 178 (1912).
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