Action of Steroidal Diamines on Active Transport and Permeability Properties of Escherichia coli

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The steroidal diamine irehdiamine A (IDA) is a potent inhibitor of bacteriophage growth and macromolecular synthesis in Escherichia coli. By using radioactive 42K and 14C-thiomethylgalactoside (TMG), rapid effects of IDA and related steroids, both on the influx of potassium and TMG via their respective transport systems and on the efflux (leakage) of radioactivity from the treated cells, have been measured. IDA affects both the influx and efflux of 42K at concentrations of steroid as low as 2 × 10−5m. Because of the increased leakage, it is not possible to tell whether there is a direct effect reducing the rate of active transport of potassium. The primary diamine, IDA, and its bis-secondary, bis-tertiary, and bis-quaternary diamine analogues are decreasingly effective in altering cell permeability properties in the order 1° > 2° > 3° > 4°. The effects of IDA on potassium transport are mirrored by similar effects on the transport of TMG. Therefore, the action of IDA is on the cell membrane and not directly on one or another transport system. The effects of IDA on cell permeability can reasonably explain the inhibitory actions of the drugs on bacteriophage growth and cellular metabolism.

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