PARTIAL-PURIFICATION OF MOLECULAR-WEIGHT 12000 FATTY-ACID BINDING-PROTEINS FROM RAT-BRAIN AND THEIR EFFECT ON SYNAPTOSOMAL NA+-DEPENDENT AMINO-ACID UPTAKE

High-affinity, Na+-dependent synaptosomal amino acid uptake systems are strongly stimulated by proteins which are known to bind fatty acids, including the MW 12,000 fatty acid binding protein (FABP) from liver. To explore the possibility that such a function might be served by fatty acid binding proteins intrinsic to brain, the 105,000g supernatant of brain was examined for fatty acid binding. Observed binding was accounted for mainly by components excluded by Sephadex G-50, and to a small degree by the MW 12,000 protein fraction (brain FABP fraction). The partially purified brain FABP fraction contained a protein immunologically identical with liver FABP as well as a FABP electrophoretically distinct from liver FABP. Brain FABP fraction markedly stimulated synaptosomal Na+-dependent, but not Na+-independent, amino acid uptake, and also completely reversed the inhibition of synaptosomal Na+-dependent amino acid uptake induced by oleic acid. Palmitic, stearic and oleic acids were endogenously associated with the brain FABP fraction. These data are consistent with the hypothesis that MW 12,000 soluble FABP intrinsic to brain may act as regulators of synaptosomal Na+-dependent amino acid uptake by sequestering free fatty acids which inhibit this process.