Uptake and Concentration of Alkylamines by a Marine Diatom

Methylamine, ethylamine, and dimethylamine (10 micromolar) are taken up and concentrated 600 to 6,000-fold by Cyclotella cryptica. Methylamine is concentrated most strongly, and its accumulation and retention are relatively insensitive to external pH but strongly inhibited by 30 millimolar external K(+). Accumulation and retention of ethyl- and dimethylamine, on the other hand, are strongly affected by external pH and less sensitive to external [K(+)]. Intracellular pH, as estimated from neutral red staining and quenching of 9-aminoacridine fluorescence, was between 4 and 5, with the central vacuole being the major acidic compartment. The accumulation of ethyl- and dimethylamine could result from diffusion of the uncharged amine across the membrane(s) and passive equilibration of the charged form (R-NH(3) (+)) inside and outside the cell. Differences in the accumulation ratio and the ion dependence for methylamine uptake relative to ethyl- and dimethylamine uptake suggests that a different mechanism is responsible for the concentration of the simpler amine.