[Conformational changes of rat liver fatty acid binding protein induced by long chain fatty acid]

Rat Liver fatty acid binding protein (FABP) has been purified to homogeneity by the procedures including Sephadex G-100 and DEAE-cellulose column chromatography. FABP was resolved into two peaks of A and B by DEAE-cellulose column chromatography. Each of these fractions exhibited apparent homogeneity upon polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate with a molecular weight of 16,000 daltons and amino acid analysis of these fractions has revealed that they are identical protein. However, upon isoelectric focusing on polyacrylamide gel, the isoelectric (pl) points were differed considerably showing microheterogeneity. In the present investigation, one isoform (pl = 5.0) of FABP was purified by a successive DEAE-cellulose column chromatography and used for the subsequent experiments of fatty acyl-protein interactions. When the final FABP preparation was partly freed of fatty acids by a mild delipidation technique using Lipidex, the pl shifted toward higher regions of 7.0. However, the pl of the delipidated FABP turned to the original 7.0 by recombining fatty acids. On the other hand, the secondary and tertiary structures were also significantly changed by delipidization, which have been demonstrated by circular dichroism (CD) and nuclear magnetic resonance (1H-NMR) spectroscopy. Furthermore the structural properties of the delipidated FABP also could be restored by recombining fatty acid. These findings suggested that the weakly bound fatty acids are responsible for the functional capacity of the FABP by virtue of changing the protein conformation.