The Entry of Ammonia into Fungal Cells

Abstract

When Scopulariopsis brevicaulis grown on an ammonia-free medium is supplied with an ammonium salt ammonia enters the cells more rapidly than it is removed by assimilation, until an equilibrium level of ammonia is reached in the cells. The equilibrium concentration in the cells is independent of metabolism and depends on the external concentration over a wide range. The internal concentra--tion of ammonia can be higher than the external under suitable conditions of pH. The cells are shown to be permeable to ammonia also in the outward direction, and the rate of entry or loss depends on the concentration difference between external and internal environment. The results support the view that ammonia enters the cells mainly by the free diffusion of the undissociated molecule.