Binding of fatty acids and peroxisome proliferators to orthologous fatty acid binding proteins from human, murine, and bovine liver

Liver-type fatty acid binding protein (L-FABP) has been proposed to be invo lved in the transport of fatty acids and peroxisome proliferators from the cytosol into the nucleus for interaction with the peroxisome proliferator-a ctivated receptors (PPARs). On the basis of this premise, we investigated b y isothermal titration calorimetry the binding of myristic, stearic, oleic, and docosahexaenoic acids to three orthologous L-FABPs and compared these results to those obtained for several xenobiotics [Wy14,643, bezafibrate, 5 ,8,11,14-eicosatetraynoic acid (ETYA), and BRL48,482] known for their perox isome proliferating activity in rodents. Recombinant human, murine, and bov ine L-FABPs were analyzed and the thermodynamic data were obtained. Our stu dies showed that fatty acids bound with a stoichiometry of 2:1, fatty acid to protein, with dissociation constants for the first binding site in the n anomolar range. With dissociation constants above 1 mu M the drug peroxisom e proliferators showed weaker binding, with the exception of arachidonate a nalogue ETYA, which bound with a similar affinity as the natural fatty acid . Some of the thermodynamic data obtained for fatty acid binding could be e xplained by differences in protein structure. Moreover, our results reveale d that binding affinities were not determined by ligand solubility in the a queous phase.