INTERACTION OF PALMITIC ACID WITH ATP ADP ANTIPORTER RECONSTITUTED INTO PROTEOLIPOSOMES/

Reconstituted adenine nucleotide transport was studied in proteoliposo mes with ATP/ADP antiporter and bacteriorhodopsin as the membrane pote ntial generator. The ADP(out)/ATP(in), exchange rate in proteoliposome s was shown to decrease at the light. This effect was reversed both by the protonophore uncoupler FCCP3 and by palmitic acid. The data are a nalyzed in terms of the electrogenicity of the ATP/ADP antiporter-medi ated nucleotide transport. Palmitic acid is suggested to increase the proton permeability of the proteoliposome membrane. The proton permeab ility of the membrane of bacteriorhodopsin-containing proteoliposomes (without ADP/ATP antiporter) is unaffected by palmitic acid. This sugg ests that fatty acids increase the proton permeability of the proteoli posome membrane after binding with ATP/ADP antiporter. Stimulation of adenine nucleotide transport by palmitic acid was also observed in the reconstituted system when the membrane potential generator was absent . Besides palmitic acid, other anionic uncouplers (DNP and FCCP) produ ce a similar, but less pronounced effect. The channel-farming peptide gramicidin D is without effect. We conclude that the observed stimulat ing effect is due to the interaction of the anionic uncoupler with the ATP/ADP antiporter rather than to an increase in the proton permeabil ity of the membrane.