occurs, even in the presence of high concentrations of potassium ions, if ammonia transporters are constitutively expressed; and (3) the physiological response of yeast to ammonium toxicity, however achieved, involves excretion of large quantities of amino acids.Potassium ions (K+; hereafter referred to as ???potassium???) are the most abundant intracellular cations in most types of cells, from S.