Abstract
Cutting and Tainter, 1 Magne, Mayer and Plantefol, 2 Hall, Field, Sahyun, Cutting and Tainter 3 and others have shown that 1-2-4 dinitrophenol (hereinafter called αDNP) increases the rate of oxygen consumption of animals by direct action on the tissue cells. Similar action on some plants has been demonstrated by Plantefol. 4 However, Genevois and Saric, 5 during the course of our experiments, reported that αDNP failed to increase yeast respiration, in fact that a concentration of 100 mg. per liter decreased respiration and the percentage of viable cells by 90%. These results .will agree with ours as to respiration if the pH was below 6.0.
We have studied the action of αDNP on the respiratory and fermentative processes of pure cultures of Saccharomyces cerevisiae, race F, over a considerable concentration range and at various acidities, using Warburg 6 respirometers at 25°C. The respiration studies were carried out in an atmosphere of pure oxygen, those on fermentation (method of Negelein 7 ) in 95% N2 and 5% CO2.
αDNP was used in the form of the sodium salt, which in no case shifted the pH from the level set by the buffers (glass electrode pH determinations were kindly made by Dr. F. DeEds). Nor did the pH level change during the course of the run.
αDNP is an acid with a pK of 4.02 at 25°C. The ions are yellow, the undissociated acid is colorless. 8 Our experiments indicate that only the undissociated form is biologically active, as the following data show.
Similar findings were obtained in the studies on fermentation. Within certain limits the action is reversible. At pH 5.9, a total concentration of 400 mg. per liter inhibits strongly. If after one hour under these conditions enough alkali is added from the side-arm of the Warburg vessel to bring to pH 6.8, thus decreasing the concentration of the undissociated form, strong stimulation results. This holds for both respiration and fermentation.
Get full access to this article
View all access options for this article.