iQ2o] ROSE, KRAYBILL, & ROSE— OXIDASE ACTIVITY 231 



The effect of the chlorides of the alkalies in retarding oxidase 

 activity suggests a possible practical application in preventing the 

 browning of fruits and vegetables during their preparation for 

 canning, preserving, or drying. 



The sulphates apparently increase oxidation slightly in all 

 cases, but the readings are not sufficiently large to be of any positive 

 significance. 



The nitrates of potassium, sodium, and magnesium have no 

 marked effect on oxidation, while the nitrates of barium, calcium, 

 manganese, and iron (ferric) decrease it. These results are similar 

 to the effect upon respiration as found by Zaleski and Reinhard 

 (33). Fernbach and Lanzenberg (13) and Kayser (20) find 

 that nitrates increase alcoholic fermentation, but, as they point out, 

 the effect may be to increase multiplication of the. yeast cells 

 rather than to affect enzymatic action. 



In tables II and III and figs. 2 and 3 are shown the oxidation 

 of pyrogallol by bark alone, by bark and carbonate, and by carbon- 

 ate alone. From these it is seen that in the last two cases oxidation 

 is considerably greater than that by the bark alone. It is also 

 seen that during the first 3 hours oxidation by carbonate is greater 

 than that by carbonate and bark, but that after the experiment 

 has stood overnight oxidation by healthy bark and carbonate 

 approaches that by carbonate alone, and oxidation by diseased 

 bark and carbonate exceeds it. 



The most obvious explanation of this fact, although possibly 

 not the true one, is that oxidation by a carbonate is a strictly 

 chemical reaction, catalyzed only by hydroxyl ions, which soon 

 comes to a definite end, while oxidation by carbonate and bark 

 is a reaction catalyzed by both " oxidase" and hydroxyl ions, in* 

 which the presence of the hydroxyl ions increases the effectiveness 

 of the " oxidase," which is slow in reaching an end-point. 



Table VI shows that tripotassium phosphate increases oxida- 

 tion of pyrogallol very markedly, both with and without bark. 

 Although no P H values for this mixture are available, we know the 

 salt is alkaline in reaction, and this effect complicates the matter. 

 With potassium dihydrogen phosphate at o . 10 N concentration a 

 decrease is evident and at o 02 N and 0.002 N concentrations a 



