Uptake of oleate by isolated rat adipocytes is mediated by a 40 kDa plasma membrane fatty acid binding protein closely related to that in liver and gut

A portion of the hepatocellular uptake of nonesterified long-chain fatty acids is mediated by a specific 40-kDa plasma membrane fatty acid binding protein, which has also been isolated from the gut. To investigate whether a similar transport process exists in other tissues with high transmembrane fatty acid fluxes, initial rates (V(o)) of [3H]-oleate uptake into isolated rat adipocytes were studied as a function of the concentration of unbound [3H)oleate in the medium. V(o) reached a maximum as the concentration of unbound oleate was increased (K(m) = 0.30 ± 0.03 μM; V(max) = 2470 ± 90 pmol/min per 5 x 104 adipocytes) and was significantly inhibited both by phloretin and by prior incubation of the cells with Pronase. A rabbit antibody to the rat liver plasma membrane fatty acid binding protein inhibited adipocyte fatty acid uptake by up to 63% in dose-dependent fashion. Inhibition was noncompetitive; at an immunoglobulin concentration of 250 μg/ml V(max) was reduced from 2480 ± 160 to 1870 ± 80 pmol/min per 5 x 104 adipocytes, with no change in K(m). A basic (pI (~) 9.1) 40-kDa adipocyte plasma membrane fatty acid binding protein, isolated from crude adipocyte plasma membrane fractions, reacted strongly in both agar gel diffusion and electrophoretic blots with the antibody raised against the corresponding hepatic plasma membrane protein. These data indicate that the uptake of oleate by rat adipocytes is mediated by a 40-kDa plasma membrane fatty acid binding protein closely related to that in liver and gut.