Plasma-membrane fatty-acid-binding protein (FABP(PM)) of the sheep placenta

Fatty acid-binding protein (FABP(pm)) has been identified and characterised from sheep placental membranes. Binding of [C-14]oleate to placental membranes was found to be time- and temperature-dependent. Addition of a 20-fold excess unlabelled oleic, palmitic, or linoleic acid reduced the binding of [C-14]oleate to the membranes to around 50% of total binding, whereas D-alpha-tocopherol at similar concentrations did not affect [C-14]oleate binding. This indicates that the binding sites are specific to fatty acids. Specific binding of [C-14]oleate was reduced by heat denaturation or trypsin digestion of the membranes, suggesting that the fatty acid-binding sites are protein in nature. FABP(pm) was then solubilised from sheep placental membranes, and subsequently purified to electrophoretic homogeneity using an oleate-agarose affinity column. The purified FABP(pm) had an apparent molecular mass of 40 kDa, as determined by SDS-PAGE and by gel permeation chromatography. The [C-14]oleate-binding activity of the purified protein was also confirmed by PAGE followed by autoradioblotting. The specific binding for oleate was around 1.5 nmol per mg of membrane protein. Our data indicate the presence of FABP(pm) in sheep placental membranes.