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Articles

Uptake and Concentration of Alkylamines by a Marine Diatom

EFFECTS OF H⁺ AND K⁺ AND IMPLICATIONS FOR THE TRANSPORT AND ACCUMULATION OF WEAK BASES ¹

Department of Botany, University of Toronto, Toronto, Ontario, Canada M5S 1A1

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-NH₃⁺) 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.

¹ This work was supported by a North Atlantic Treaty Organization Postdoctoral Fellowship (to P.A.W.), by National Research Council of Canada Grant A 6032 (to J.A.H.), and by National Science Foundation Grant OCE 78-26011 (to J. J. McCarthy).