Ammonia accumulation in acetate-growing yeast.
During growth on acetate, the pH of yeast cultures rises from 5.8 to around 7-8 in the stationary phase. This was found to result from acetic acid uptake and accompanying H+ loss. In addition, acetate-growing yeast were found to accumulate ammonia. The influence of pH on ammonia transport and accumulation was studied with the analogue [14C]methylamine with the following results. (a) Methylamine uptake kinetics from 0.1-50 mM were consistent with a single-component uptake system (NH+4 permease) at pH values more acidic than 6.5, and with a two-component system (NH+4 permease and NH3 diffusion) above pH 7.5. (b) Equilibrium accumulation of methylamine was found to increase with increasing pH. (c) Methylamine efflux from methylamine-loaded cells increased as the external pH decreased. It was concluded from measurements of the internal pH under various culture conditions that the accumulation of ammonia in acetate-growing alkaline cultures resulted from the sum of two processes: (1) an energy-driven NH+4 transport; and (2) NH3 diffusion dependent on the delta pH.
D000085:Acetates / Q000378:metabolism*; D000641:Ammonia / Q000378:metabolism*; D001692:Biological Transport; D005971:Glutamates / Q000378:metabolism; D018698:Glutamic Acid; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008744:Methylamines / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000254:growth & development* / Q000378:metabolism
D000085:Acetates; D005971:Glutamates; D008744:Methylamines; D018698:Glutamic Acid; D000641:Ammonia; C027451:methylamine