Transport of Fe2+ across lipid bilayers: possible role of free fatty acids.

Fatty acids can form lipid-soluble complexes with Fe2+. Incorporation of fatty acids into phosphatidylcholine/cholesterol liposomes renders them permeable to Fe2+. Of several fatty acids tested, the most effective Fe2+ carriers were linoleic and oleic acids followed, in decreasing order of efficacy, by linolenic, myristic, arachidonic and palmitic acids. The initial Fe2+ transport rate for oleic acid depends on free Fe2+ in the medium which in turn shows a strong pH dependence above pH 7.0. The overall pH dependence of Fe2+ transport for several fatty acids shows an optimum near 6.9. Fe2+ transport catalysed by oleic acid can be inhibited by high NaCl concentrations but not 1 mM Co2+. It is suggested that free fatty acids may act as mediators of Fe2+ transport across biological membranes, particularly isolated intestinal brush-border membrane.