The uptake of amino acids by particulate fractions from brain

Abstract

1. 1. Crude nuclear and mitochondrial fractions from rat brain, upon incubation in appropriate media, take up amino acids against a concentration gradient, with equilibrium reached in most cases within 60 min. 2. 2. The various amino acids are taken up to different degrees; those that are high in the living brain, such a glutamate, γ-aminobutyric acid, and glycine, are taken up by the particulate fractions to higher levels than the amino acids at lower levels in the living brain. 3. 3. Uptake seems to be energy dependent: CN − and 2,4-dinitrophenol strongly, although not completely, inhibit uptake; and concentrative uptake is absent at 0° for most amino acids. 4. 4. Uptake is dependent on the composition of the medium. Ouabain inhibits uptake; low Na + concentration in the medium, which reduces particulate Na + and K + concentration, is also inhibitory. Ca 2+ is not an absolute requirement, but it increases uptake. 5. 5. Glutamate uptake is inhibited by aspartic acid, but not significantly by other amino acids. The uptake of other amino acids also shows some substrate specificity. 6. 6. In mitochondrial subfractions from brain, nerve-ending particles are the most active in uptake; but under suitable conditions purified mitochondria also show uptake against a concentration gradient. 7. 7. The uptake by particulate fractions seem to be fairly specific for brain particulate fractions from newborn and adult brain showed uptake against a concentration gradient, but those from the other organs tried: liver, muscle and kidney, did not.