EFFECTS OF ACETIC-ACID ON RESPIRATION OF DEBARYOMYCES-HANSENII .3. STUDIES ON THE MECHANISMS OF THE ANTIFUNGAL ACTION OF ACETIC-ACID

To elucidate a mechanism of the inhibitory action of acetic acid on re spiration in yeast, Debaryomyces hansenii, transport of acetic acid in to cells and effects of acetic acid on enzymes in a TCA cycle were inv estigated. (1) D. hansenii cells grown in the medium containing 0.2 M of acetic acid, intracellular concentration of acetic acid increased t o about 20-fold over that of the cells suspended in the absence of ace tic acid. This result indicated that acetic acid in the medium was tra nsported into cells, resulting in accumulation of acetic acid in cells in a large quantity. (2) On the cells grown in medium containing 0.33 M of acetic acid, concentration of all organic acids in a TCA cycle d ecreased compared with that of the cells grown in the absence of aceti c acid in cells and media. (3) Among the TCA cycle enzymes 2-oxoglutar ate dehydrogenase complex and pyruvate dehydrogenase complex (PDHC) we re found to be severely inhibited by 200 mM acetic acid, and PDHC was inhibited completely even by 0.2 mM acetic acid. These results suggest ed that PDHC primarily inhibited by acetic acid accumulating in cells, resulting in the decrease in organic acids in a TCA cycle and the gro wth inhibition.