[Energy-dependent uptake of thallium by Chlorella]

Abstract

The uptake of labelled thallous ion into the interior of Chlorella fusca is enhanced by light. This is ascribed to active transport by way of the K (and Rb) pump. The Michaelis constants differ between the higher and the lower concentration ranges, but they are similar for Rb and Tl.The additional, rapid, light-independent adsorption of Tl, mainly by the cell wall, is stronger than that of the alkali ions, but weaker than that of divalent cations. The adsorbed Tl is subject to elution by complexing agents (probably mainly glycolic acid) secreted by the cells, especially in the light.In spite of the similarity of the Michaelis constants, the inhibition of the light-dependent uptake of labelled Rb by unlabelled Tl is far stronger than the inhibition of Tl uptake by Rb. The efficiency of Tl may be due to double action: namely, competition with Rb for the carrier and negative influence on a transport ATPase.