1. When guinea-pig cerebral-cortex slices were incubated with [U−14C]glutamate as substrate, the specific radioactivities of the citric acid-cycle intermediates were lower than that of the aspartate isolated from the same vessels. 2. Aspartate was significantly labelled when [5−14C]glutamate was used as substrate and the aspartate contained almost no label when [1−14C]glutamate was present as substrate. 3. When specifically labelled glutamate was used as substrate, the label was found in the isolated aspartate in the position that would be predicted by citric acid-cycle mechanisms. 4. The results are consistent with the theory of ‘compartmentation’ of amino acid metabolism.
