1. The excretion of H+ ions, with practically equivalent uptake of K+ ions (from 0·1m-potassium chloride), occurs during the aerobic oxidation of ethanol. 2. Acetaldehyde and acetic acid formed at the same time are quantitatively equal to the amount of ethanol oxidized. 3. A slow uptake of K+ ions occurs during the oxidation of acetaldehyde and a more rapid uptake during the oxidation of d-glyceraldehyde 3-phosphate. 4. The anaerobic reduction of methylene blue is studied, and the inhibitory effect of K+ and other inorganic cations on the system demonstrated. 5. The cation requirement for equal inhibitory effect is parallel with the reciprocals of the transport affinities for the ‘physiological K-carrier’ (as taken from Conway & Duggan, 1958). 6. The cation inhibition of methylene blue reduction is reversed by treatment of the yeast with Teepol or by freezing-and-thawing. 7. Azide is shown to inhibit the reduction of methylene blue with intact cells. The inhibition is partially reversed by Teepol treatment and completely by freezing-and-thawing.
