ACTIVITY OF THE PLASMA-MEMBRANE H-ATPASE AND OPTIMAL GLYCOLYTIC FLUX ARE REQUIRED FOR RAPID ADAPTATION AND GROWTH OF SACCHAROMYCES-CEREVISIAE IN THE PRESENCE OF THE WEAK-ACID PRESERVATIVE SORBIC ACID()

The weak acid sorbic acid transiently inhibited the growth of Saccharo myces cerevisiae in media at low pH, During a lag period, the length o f which depended on the severity of this weak-acid stress, yeast cells appeared to adapt to this stress, eventually recovering and growing n ormally, This adaptation to weak-acid stress was not due to metabolism and removal of the sorbic acid, A pmal-205 mutant, with about half th e normal membrane H+-ATPase activity, was shown to be more sensitive t o sorbic acid than its parent, Sorbic acid appeared to stimulate plasm a membrane H+-ATPase activity in both PMA1 and pmaI-205, Consistent wi th this, cellular ATP levels showed drastic reductions, the extent of which depended on the severity of weak-acid stress, The weak acid did not appear to affect the synthesis of ATP because CO2 production and O -2 consumption were not affected significantly in PMA1 and pmaI-205 ce lls, However, a glycolytic mutant, with about one-third the normal pyr uvate kinase and phosphofructokinase activity and hence a reduced capa city to generate ATP, was more sensitive to sorbic acid than its isoge nic parent, These data are consistent with the idea that adaptation by yeast cells to sorbic acid is dependent on (i) the restoration of int ernal pH via the export of protons by the membrane H+-ATPase in an ene rgy-demanding process and (ii) the generation of sufficient ATP to dri ve this process and still allow growth.