Specific high-affinity binding of fatty acids to epidermal cytosolic proteins

Cytosol from rat, mouse, and human skin or rat epidermis was incubated with [³h]arachidonic acid, [¹⁴C]retinoic acid, [¹⁴C]oleic acid, [³H]leukotriene A₄, [³H]prostaglandin E₂ (PGE₂) or [³H]15-hydroxyeicosatetraenoic acid (15-HETE), and protein-bound ligands were separated using Lipidex-1000 at 4°C to assess the binding specificity. The binding of oleic acid and arachidonic acid with rat epidermal cytosol was rapid, saturable, and reversible. Binding of oleic acid was competed out with the simultaneous addition of other ligands and found to be in the following order: arachidonic acid > oleic acid > linoleic acid > lauric acid > leukotriene A₄ > 15-HETE = PGE₂ > PGE₂ = PGF₂ = PGD₂. Scatchard analysis of the binding with arachidonic acid, oleic acid, and retinoic acid revealed high-affinity binding sites with the dissociation constant in the nM range. SDS-PAGE analysis of the oleic acid-bound epidermal cytosolic protein(s) revealed maximum binding at the 14.5 kDa region. The presence of the fatty acid-binding protein in epidermal cytosol and its binding to fatty acids and retinoic acid may be of significance both in the trafficking and the metabolism of fatty acids and retinoids across the skin.