Formation of extracellular glutamate from glutamine: exclusion of pyroglutamate as an intermediate.
Formation of extracellular glutamate from glutamine: exclusion of pyroglutamate as an intermediate.
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从谷氨酰胺形成细胞外谷氨酸：排除焦谷氨酸作为中间体。
DOI：
10.1016/j.brainres.2005.06.014
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发表时间：
2005
期刊：
影响因子：
--
通讯作者：
Zielke,HRonald
中科院分区：
文献类型：
--
作者：
Mena,FernandoV;Baab,PeterJ;Zielke,CarolL;Huang,Yinyin;Zielke,HRonald
5 mM谷氨酰胺反向微透析进入大鼠海马后，间质谷氨酸增加4.6倍。研究了谷氨酰胺水解的两种可能机制：(a)酶促谷氨酰胺酶活性和(b)非酶促机制。在微透析部位注射14c -谷氨酰胺，然后用人工脑脊液进行微透析，可以分离出14c -谷氨酰胺（63%）、14c -谷氨酸（14%）和一种初步鉴定为焦谷氨酸（22%）的化合物。在这项研究中，我们确定了谷氨酰胺非酶促焦谷氨酸形成是否有助于谷氨酸的合成。焦谷氨酸与谷氨酸处于化学平衡，但在生理条件下，化学平衡强烈偏向焦谷氨酸方向。体外稳定性研究表明，14c -谷氨酰胺和14c -焦谷氨酸在pH 6.5-7.5、37°C、长达8小时的条件下不会发生显著的非酶促分解。用1mm焦谷氨酸进行反向微透析不会增加间质谷氨酸水平。注射14c -焦谷氨酸和微透析后，14c -焦谷氨酸（88%）和14c -谷氨酰胺（11%）的放射性恢复。不到1%的放射性物质被回收为谷氨酸。我们的数据不支持焦谷氨酸在输注谷氨酰胺后形成细胞外谷氨酸的中间体的作用。然而，它证实了焦谷氨酸，一种已知的大脑成分，在脑细胞中被积极代谢，并在间质空间中贡献谷氨酰胺。
A 4.6-fold increase in interstitial glutamate was observed following the reverse microdialysis of 5 mM glutamine into the rat hippocampus. Two possible mechanisms of glutamine hydrolysis were examined: (a) an enzymatic glutaminase activity and (b) a non-enzymatic mechanism. Injection of14C-glutamine at the site of microdialysis followed by microdialysis with artificial cerebral spinal fluid allowed isolation of14C-glutamine (63%),14C-glutamate (14%), and a compound tentatively identified as pyroglutamate (22%). In this study, we determined if non-enzymatic pyroglutamate formation from glutamine contributed to the synthesis of glutamate. Pyroglutamate is in chemical equilibrium with glutamate, although under physiological conditions, the chemical equilibrium is strongly in the direction of pyroglutamate. In vitro stability studies indicated that14C-glutamine and14C-pyroglutamate are not subject to significant non-enzymatic breakdown at pH 6.5–7.5 at 37 °C for up to 8 h. Reverse microdialysis with 1 mM pyroglutamate did not increase interstitial glutamate levels. Following injection of14C-pyroglutamate and microdialysis, radioactivity was recovered in14C-pyroglutamate (88%) and14C-glutamine (11%). Less than 1% of the radioactivity was recovered as glutamate. Our data do not support a role of pyroglutamate as an intermediate in the formation of extracellular glutamate following the infusion of glutamine. However, it confirms that pyroglutamate, a known constituent in brain, is actively metabolized in brain cells and contributes to glutamine in the interstitial space.