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

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.