GO 
FIFTEENTH REPORT. 
THE NATURE OF ENZYME ACTION. 
BY JAMES GORDON CUMMING, M. D., IN CHARGE OF TFIE PASTEUR INSTITUTE 
OF THE UNIVERSITY OF MICHIGAN, ANN ARBOR. 
One of the most striking characteristics of the living cell is the ease 
with which its products of metabolism split bodies of a highly stable 
nature. Soluble starch, for example, is hydrolyzed to the simple sugars 
by ptyalin. Egg-white is split into comparatively simple compounds 
by pepsin hydrochloric acid. Under ordinary laboratory conditions, on 
the other hand, powerful reagents and high temperature are required 
to accomplish these decompositions. The digestion of the food stuffs 
is recognized as a process of fermentation or enzyme action. The enzymes 
have not as yet been isolated in pure form ; consequently we have no 
definite knowledge concerning their chemical constitution, nor the exact 
character of their action. 
In seeking an explanation of ferment action one naturally turns to 
certain simple chemical reactions which are apparently similar in their 
essentials. These are termed catalytic reactions and were recognized as 
early as 1834 by Mitscherlich. He stated that the formation of ethyl 
ether and water from ethyl alcohol in the presence of sulphuric acid 
did not depend upon the dehydrating power of the acid nor upon the 
formation of an intermediate product, ethyl sulphuric acid, but that 
the acid facilitated the reaction by its mere presence without entering 
into it. He called this “contact action*’ a designation which is in every 
way as appropriate as catalysis, which term was suggested by Berzelius 
in 1835. 
Let us consider briefly this phenomenon, contact action or catalysis. 
It is found that oxygen and hydrogen at ordinary temperatures com- 
bine so slowly that the production of water cannot be detected. But 
the presence of finely divided platinum is sufficient to cause combination 
to take place rapidly. Again, the oxidation effected by hydrogen perox- 
ide proceeds in many cases at a very slow rate, but this can be en- 
ormously accelerated by traces of iron or manganese. The oxidation of 
sulphur dioxide to sulphur trioxide occurs but slowly. In the presence 
of oxides of nitrogen the velocity of the reaction is greatly accelerated. 
The contact process for the manufacture of sulphuric acid depends upon 
finely divided platinum or iron oxide as catalytic agents. The manu- 
facture of glucose from starch depends upon dilute acids as catalyzers, 
and in the Deacon process copper chloride hastens the combination of 
hydrogen and chlorine to hydrochloric acid. 
Although the work accomplished by these catalysts is strikingly simi- 
lar to that of the ferments, yet it is not analogous in every respect. 
Exact proportions are not required between catalyst and substrate nor 
between enzyme and substrate. In extremely high dilutions of either 
catalyst or enzyme the reaction proceeds even though the rate may be 
slower than in more concentrated solutions. In these two respects they 
are similar.' 
