Placental membrane fatty acid-binding protein preferentially binds arachidonic and docosahexaenoic acids

To elucidate further the role of placental membrane fatty acid-binding protein (p-FABP(pm)) in preferential transfer of maternal plasma long chain polyunsaturated fatty acids (LCPUFA) across the human placenta, direct binding of the purified protein with various radiolabelled fatty acids (docosahexaenoic, arachidonic, linoleic and oleic acids) was investigated. Binding of these fatty acids to the protein revealed that p-FABP(pm) had higher affinities and binding capacities for arachidonic and docosahexaenoic acids compared with linoleic and oleic acids. The apparent binding capacities (B-max) values for oleic, linoleic, arachidonic and docosahexaenoic acids were 2.0 +/- 0.14, 2.1 +/- 0.17, 3.5 +/- 0.11, 4.0 +/- 0.10 mol per mol of p-FABP(pm) whereas the apparent dissociation constant (K-d) values were 1.0 +/- 07, 0.73 +/- 0.04, 0.45 +/- 0.03 and 0.4 +/- 0.02 mu M, respectively (n=3). In the case of human serum albumin, the K-d and B-max values for all fatty acids were around 1 mu M and 5 mol/mol of protein, respectively. These data provide direct evidence for the role of p-FABP(pm) in preferential sequestration of maternal arachidonic and docosahexaenoic acids by the placenta for transport to the fetus by virtue of its preferential binding of these fatty acids.