大脑中谷氨酸代谢的区室化。大脑中存在两种不同三羧酸循环的证据。

(14)C from [1-(14)C]glucose injected intraperitoneally into mice is incorporated into glutamate, aspartate and glutamine in the brain to a much greater extent than (14)C from [2-(14)C]glucose. This difference for [1-(14)C]glucose and [2-(14)C]glucose increases with time. The amount of (14)C in C-1 of glutamate increases steadily with time with both precursors. It is suggested that a large part of the glutamate and aspartate pools in brain are in close contact with intermediates of a fast-turning tricarboxylic acid cycle. 2. (14)C from [1-(14)C]acetate and [2-(14)C]acetate is incorporated to a much larger extent into glutamine than into glutamate. An examination of the time-course of (14)C incorporated into glutamine and glutamate reveals that glutamine is not formed from the glutamate pool, labelled extensively by glucose, but from a small glutamate pool. This small glutamate pool is not derived from an intermediate of a fast-turning tricarboxylic acid cycle. 3. It is proposed that two different tricarboxylic acid cycles exist in brain.

腹腔注射[1-(¹⁴)C]葡萄糖后，小鼠脑中的¹⁴C掺入谷氨酸、天冬氨酸和谷氨酰胺的程度，比[2-(¹⁴)C]葡萄糖中的¹⁴C掺入这些物质的程度要大得多。[1-(¹⁴)C]葡萄糖和[2-(¹⁴)C]葡萄糖的这种差异随时间增加。两种前体物质存在时，谷氨酸C-1位的¹⁴C含量均随时间稳步增加。这表明脑中谷氨酸和天冬氨酸池的很大一部分与快速运转的三羧酸循环的中间产物密切接触。2. [1-(¹⁴)C]乙酸盐和[2-(¹⁴)C]乙酸盐中的¹⁴C掺入谷氨酰胺的程度比掺入谷氨酸的程度大得多。对掺入谷氨酰胺和谷氨酸的¹⁴C的时间进程进行检查发现，谷氨酰胺不是由被葡萄糖大量标记的谷氨酸池形成的，而是由一个小的谷氨酸池形成的。这个小的谷氨酸池不是来自快速运转的三羧酸循环的中间产物。3. 有人提出脑中存在两种不同的三羧酸循环。

Compartmentation of glutamate metabolism in brain. Evidence for the existence of two different tricarboxylic acid cycles in brain.