Alteration of delta psi-dependent amino acid transports in Streptococcus pneumoniae by the antitumoral drug SOAz.

Interactions of the antitumoral drug SOAz with natural and model membranes are described. Biological studies were carried out with the bacterium Streptococcus pneumoniae taken as a model system. They reveal that SOAz is able to reduce delta psi and the delta psi-dependent amino acid transports without being cytotoxic for the bacteria. With respect to model membranes, leakage studies carried out with Na+ and K+ loaded lipid vesicles demonstrated that SOAz exhibits no ionophore activity. In contrast, the drug is shown to decrease the surface potential of monolayers of acidic phospholipids but without penetrating within the film. The possibility that SOAz might alter the delta psi part of the proton motive force by decreasing the outside surface potential of the bacterial membrane is discussed.