Effect of 2–4 Dinitrophenol on Inhibition of Yeast Respiration by Cyanide. ∗

Tainter and coworkers 1 , 2 and others 3 have shown that 2–4 dinitrophenol (alpha-DNP) stimulates respiration in animals by direct action on the tissue cells. We have shown previously that this substance stimulates or inhibits respiration and fermentation of yeast (Saccharomyces cerevisiae, Race F) depending upon the concentration of the undissociated acid form. 4 , 5

The experimental procedure used in the present study has been described elsewhere. 4 , 5

Treatment of yeast suspended in glucose phosphate media with M/1000 NaCN of the same pH reduces respiration to about 14% of the control rate. If alpha-DNP be now added in a dose which causes optimal stimulation of the cyanide-free yeast, i. e., in amount giving a free acid alpha-DNP concentration of 0.64 mg. per liter at pH 6.8, 5 it further depresses the respiration of the yeast poisoned with cyanide.

However, the respiration of yeast poisoned with cyanide can be stimulated by alpha-DNP, provided that the concentration of the undissociated acid form of this agent be approximately 0.032 mg. per liter, i. e., about 1/20 of the optimal dose for unpoisoned yeast. Under these conditions the respiratory rate of the poisoned yeast may be increased by about 20%. This relation has been demonstrated at pH 5.9 and pH 6.8. Further experiments on the action of alpha-DNP on respiration of organisms and tissues poisoned by cyanide are in progress.