Characterization of the non-constitutive ethanesulfonate uptake in Chlorella fusca

Abstract

Ethanesulfonate entered Chlorella fusca via a temperature-, pH-, energy-, and concentration-dependent system ('permease'). Transport was unidirectional and followed hyperbolic saturation kinetics with a Michaelis-Menten constant of 5 · 10-5 M. Uptake was substantially inhibited by structural analogues, indicating a high specificity for the sulfonate group in the compounds tested. Furthermore the permease could clearly distinguish between other monovalent anions, monocarboxylates or sulfate, indicating a distinct uptake system in this alga. The negative effect of several metabolic inhibitors and SH-group reagents on ethanesulfonate uptake was evident. Ethanesulfonate uptake could be enhanced by polyvalent cations apparently via reduction of the surface potential and could be strongly stimulated by addition of phosphate ions to the medium. Radioactive labelled ethanesulfonate was rapidly metabolized to sulfate, the main and probably the first degradation product of ethanesulfonic acid in Chlorella fusca. © 1986.