THE TARGET OF AMMONIA ACTION IN DICTYOSTELIUM

The weak base ammonia is implicated in a number of key processes in Di ctyostelium development, notably aggregation and culmination. To deter mine its intracellular site of action, we compared its biological pote ncy with that of other weak bases. All the bases inhibited these devel opmental processes effectively, but differed manyfold in potency in ac cordance with their activity in dissipating pH gradients, as measured by in vivo P-31 NMR with pH-sensitive phosphonate probes. These result s indicate that weak bases influence development by raising the pH of an intracellular acidic compartment.