Kinetic evidence for duplicity in ion transport

In this paper, we report the results of a kinetic investigation of the ion transport properties of four sterol-oligo (ethylene glycol) conjugates that have been modeled after the heptaene macrolide antibiotic, Amphotericin B. Specifically, we report the activity of 1, 2, 3, and 4 in promoting the transport of Na+ across egg phosphatidylcholine bilayers as a function of their membrane concentration. Our kinetic results not only provide compelling evidence for the existence of two discrete forms of an active ionophore in each case but also serve as a cautionary note for interpreting ionophoric activity based on single-concentration experiments.