Fatty-acid-binding protein facilitates the diffusion of oleate in a model cytosol system.

The proposed function of fatty-acid-binding proteins in facilitating the diffusion of their ligand has been examined in a cytosolic model using a steady-state diaphragm cell apparatus. The white muscle of ocean pout (Macrozoarces americanus) does not have a fatty-acid-binding protein: nor does it exhibit detectable beta-oxidative capacity, and as such is a good source of cytosol preparation. After determining the diffusion coefficient of oleate in this medium, fatty-acid-binding protein, isolated from the ventricle of this animal, was added and the apparent diffusion coefficient was again determined. The presence of the fatty-acid-binding protein increased the apparent diffusion coefficient of this long-chain fatty acid about 6-fold, from 0.087 x 10(-5) cm2.s-1 to 0.58 x 10(-5)cm2.s-1. This confirms the facilitated diffusion hypothesis as one role of fatty-acid-binding protein. The diffusion coefficients of oleate in 50 mM-sodium phosphate buffer, pH 7.4, at 10 degrees C and 25 degrees C (0.15 x 10(-5) cm2.s-1 and 0.28 x 10(-5) cm2.s-1 respectively) were also measured.