LIPID A, VARIOUS FATTY ACIDS, AND THEIR DERIVATIVES AS PROTON CONDUCTORS IN MEMBRANE VESICLES FROM ESCHERICHIA COLI

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The mechanism of inhibition by lipid A, various fatty acids, or their derivatives on the transport activities of membrane vesicles from Escherichia coil was studied. Various fatty acids and lauryl alcohol dramatically enhanced the proton permeability of membrane vesicles, potently inhibited the uptake of triphenylmethylphosphonium ion by the membrane vesicles, and severely inhibited the uptake of serine driven by an artificial membrane potential introduced by K⁺-diffusion via valinomycin. Lipid A and methyl laurate also acted similarly to fatty acids although to a lesser extent.
It was also found that the inhibition of transport activities by lipid A and fatty acids was partially recovered by the addition of bovine serum albumin. Bovine serum albumin removed fatty acid from fatty acid-treated membrane vesicles and reduced the proton permeability compared to the treated membrane vesicles.
These results indicated that lipid A, fatty acids, and their derivatives acted as proton conductors of membrane vesicles. The proton potential (interior negative) produced by electron transport systems or by K⁺-valinomycin was abolished in the presence of these compounds. For this reason, neither succinate nor amino acids could be accumulated by membrane vesicles in the presence of lipid A, fatty acids, or their derivatives.