Mechanism of conversion of aspartate into glutamate in cerebral-cortex slices

Abstract

1. When slices of guinea-pig cerebral-cortex slices are incubated with [U-(14)C]-aspartate and non-radioactive glucose as substrates, the specific radioactivities of the citric acid-cycle intermediates are lower than that of the glutamate isolated from the same vessels. 2. Glutamate was significantly labelled when [1-(14)C]-aspartate and glucose were present in the incubation medium. These results would not be expected on the basis of simple conversion of aspartate into glutamate through the citric acid cycle, since the C-1 position of oxaloacetate is decarboxylated in the conversion of isocitrate into alpha-oxoglutarate. 3. It appears that aspartate is converted into glutamate by citric acid-cycle mechanisms; however, the carbon ;skeleton' is not immediately condensed with acetyl-CoA to form citrate but first follows the cycle in a reverse direction to fumarate or succinate and then proceeds in the forward direction. 4. The conversion of aspartate into glutamate appears to be compartmentalized.

Cross‐Species Comparison of Metabolite Profiles in Chemosensory Epithelia: An Indication of Metabolite Roles in Chemosensory Cells

“…Aspartate is important for conversion to glutamate (Simon et al, 1967). In some species, there is evidence for a role in neurotransmission (Shank et al, 1975; Constanti and Nistri, 1978; D'Aniello et al, 2005).…”

Conversion of glutamate into aspartate in guinea-pig cerebral-cortex slices

“…DL-[5-14C]Glutamic acid was purchased from Nichem Inc. (Bethesda, Md., U.S.A.). All substrates and radioactive tracers were purified as reported by Simon, Drori & Cohen (1967).…”

“…and placed in Warburg vessels (two slices/vessel) containing 3ml. ofthe incubation medium (Elliot's saline buffer, pH 7-4; Simon et al 1967). The vessels were incubated for 1-5hr.…”

“…The tissue and medium from the appropriate vessels were pooled and homogenized, and the amino acids and citric acid-cycle intermediates were extracted, separated and determined. The details of the methods were as described by Simon et al (1967). The only change in the incubation conditions involved the substrate, [14C]glutamic acid (20,umoles/vessel, 3,uc) being utilized as the sole added substrate in place of aspartate plus glucose.…”

“…mounted on an automatic amino acid analyser (Beckman Instrument Co., Palo Alto, Calif., U.S.A.). The appropriate fraction containing aspartate was desalted by passing it through a Dowex 50 column, the salts were eluted with water and the amino acid was eluted with 2 N-NH3 (Simon et al 1967 Meister, Sober & Tice (1951). The CO2 evolved from C-1 of aspartate was trapped in the centre well of a Warburg incubation vessel.…”