Fatty acid binding protein from rat heart. The fatty acid binding proteins from rat heart and liver are different proteins.

The binding of [3H]oleic acid and [3H]palmitic acid to the low molecular weight fatty acid binding proteins present in the cytosols of rat liver and heart was studied. Both fatty acids were bound by Z protein of liver, whereas only oleic acid was bound by the fraction of heart that contains the fatty acid binding protein. However, after delipidation of heart cytosolic proteins with butanol, the binding of palmitic acid to the fatty acid binding protein was detected. In contrast to a published report (Gloster, J., and Harris, P. (1977) Biochem. Biophys. Res. Commun. 74, 506-513), oleic acid was not bound by rat heart or bovine heart myoglobin. Both rat heart fatty acid binding protein and rat liver Z protein were purified to homogeneity or near homogeneity. On polyacrylamide gel electrophoresis under nondenaturing conditions, liver Z protein gave rise to three bands, none of which was identical with the single band due to heart fatty acid binding protein. Rabbit antibodies to rat liver Z protein were used to demonstrate that the purified fatty acid binding protein from rat liver (Z protein) and rat heart are immunologically unrelated and that no Z protein is present in rat heart cytosol. Taken together, these observations lead to the conclusion that the low molecular weight fatty acid binding proteins from rat liver and heart are different proteins.