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Abstract —(1) Compartmentation of the metabolism of amino acids in brain has been studied in slices of cerebral cortex incubated with sodium 1‐ 14 Cacetate, sodium 1‐ 14 C‐bicarbonate, 1‐ 14 CGABA or l‐1‐ 14 Cglutamate and in samples of brain after injection in vivo of 1‐ 14 C‐ or 3 Hacetate. (2) The method of treatment of the slices (a) maintained in ice‐cold medium prior to incubation; (b) preincubation at 37°C and transfer to fresh medium affected the metabolism of the added, labelled substrate, particularly its labelling of glutamine. (3) The specific activity of glutamine labelled from the above metabolites was greater than that of glutamic acid in experiments of 10–30 minutes duration, whether or not subjected to pretreatment in the cold. (4) Incubation in medium containing 27 mm‐K + was associated with a decrease in the relative specific activity (RSA) of glutamine, except for the increase when l‐1‐ 14 Cglutamate was the precursor. (5) The data have been discussed in terms of metabolic compartmentation and their consistency with the concept of the presence in brain of more than one citric acid cycle, one containing the relatively smaller pools of intermediates and associated with synthetic processes; the other containing the relatively larger pools of intermediates and functioning as a homeostatic buffer for energy metabolism.
Berl et al. (1970) studied this question.