Uptake and Concentration of Alkylamines by a Marine Diatom

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Abstract
Methylamine, ethylamine and dimethylamine (10 .mu.M) are taken up and concentrated 600- to 6000-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 .mu.M external K+. Accumulation and retention of ethyl- and dimethylamine 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 may result from diffusion of the uncharged amine across the membrane(s) and passive equilibration of the charged form (R-NH3+) inside and outside the cell. Differences in the accumulation ratio and the ion dependence for methylamine uptake relative to ethyl- and methylamine uptake suggests that a different mechanism is responsible for the concentration of the simpler amine.