Comparison of Capacity of Some Nitrated Phenols to Stimulate Respiration of Yeast. ∗

We have shown that the action of several of the nitrated phenols on the respiration of yeast may be excitatory or inhibitory, depending on the dosage, and that the undissociated form is the active agent in such stimulation or inhibition. 1 , 2 , 3 A method for comparing the activities of nitrated phenols as metabolic stimulants has been developed and applied to 3 of the dinitrophenols and to the mononitrophenols. 3 We present herewith the results of experiments designed to compare the activities of 5 nitrated phenols which have been used extensively as metabolic stimulants. These are 2–4 dinitrophenol, 4 4–6 dinitro-o-cresol, 5 2–4 dinitro-α-naphthol, 6 2–4 dinitro-cyclo-pentyl phenol 6 and 2–4 dinitro-cyclo-hexyl phenol. 6 The last 2 compounds were provided through the kindness of Dr. M. L. Tainter, who obtained them from Hoffman, LaRoche and Company. In every case aqueous solutions of the sodium salts were employed.

The pure yeast culture and the experimental methods have been described elsewhere. 2 , 3 In every case the yeast, after preliminary washing, was suspended in 1% glucose made up in 0.1M phosphate buffer, pH 6.8, and the respiratory rate was measured in the conventional form of Warburg manometer in a water bath at 25 ± 0.02°C. Each series of comparisons involving the 5 compounds was performed on yeast from a single Orla-Jensen plate, incubated for 96 hours at 25°C.

The concentrations of the nitrated phenols which evoked maximal stimulation of yeast respiration in glucose-phosphate (optimal concentrations) were determined in a series of 6 to 12 preliminary experiments on each compound. These concentrations are given in Table I, together with average values for the control and experimental respiratory rates n 2 series of comparisons.