[Interaction of palmitic acid with the ADP/ATP antiporter, reconstituted in liposomes]

Reconstituted adenine nucleotide transport has been studied in proteoliposomes with the ADP/ATP antiporter and bacteriorhodopsin as the membrane potential generator. The ADP(out)/ATP(in) exchange rate in the model system decreased after illumination of the proteoliposomes. This effect was reversed by both protonophore FCCP and palmitic acid. The data obtained are analysed in terms of the electrogeneity of the nucleotide transport by the antiporter. It is suggested that palmitic acid increases the conductivity of the proteoliposome membrane. The membrane conductivity of bacteriorhodopsin proteoliposomes (without the ADP/ATP antiporter) is unaffected by palmitic acid. Seemingly, the ADP/ATP antiporter mediated increase of the proteoliposomal membrane conductivity is induced by fatty acids. Stimulation of the adenine nucleotide transport by fatty acids was also observed in the reconstituted system, when the membrane potential was absent. Besides palmitic acid, other anionic uncouplers, DNP and FCCP, produce a similar, however, less pronounced effect. Gramicidin D is without effect. It is concluded that the observed stimulating effect is due to the anionic uncoupler interaction with the ADP/ATP antiporter rather than to the membrane proton conductivity increase.