RELATION OF OXIDASES AND CATALASE TO RESPIRA- 
TION IN PLANTS 
Charles O. Appleman 
The chemical mechanism of respiration in plants is very complex 
and imperfectly understood. It is a product of the living cells and 
is capable of bringing about, at low temperatures, the oxidation of 
organic substances which, in the laboratory, are oxidized only by 
employing very high temperatures and powerful reagents. 
The presence of oxygen activators and carriers in plants has long 
been recognized and Traube as early as 1877 called these substances 
oxidizing ferments. Bertrand^ was led to believe that the oxidizing 
ferments are more or less specific in their action,, so he proposed the 
term oxidases as a group name for these ferments. Oppenheimer^^ 
has classed the oxidation enzymes according to the substances now 
generally recognized as acted upon by these enzymes. He realizes, 
however, the provisional character of such a classification and states 
further that the oxidation ferments represent the darkest Africa in 
the ferment world. The phenolases of Oppenheimer's classification 
accelerate only the oxidation of aromatic substances and are thus the 
oxidizing enzymes that are measured by the oxidase reagents in com- 
mon use at the present time. The oxidases referred to in this paper 
include only the phenolases of Oppenheimer's classification. 
Practically all attempts to explain the mechanism of respiration 
have assigned these long-established oxidative forces in the cell a 
role in this process, although such a relationship is almost entirely 
hypothetical. The chief difficulty lies in the fact that the oxidases, 
as detected and measured by the prevailing methods, have no direct 
action on the ordinary substances consumed in respiration, as sugar, 
for example. When it was recognized that respiration occurs in two 
distinct stages: namely, an anaerobic and aerobic stage, the oxidases 
were relieved of the responsibility of direct oxidation of these complex 
organic substances; since on this basis they would be concerned only 
in the oxidation of the decomposition products of the anaerobic stage. 
But all the known products of this stage are aliphatic substances 
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