Kanamori K, Ross B D
Magnetic Resonance Spectroscopy Laboratory, Huntington Medical Research Institutes, Pasadena, California 91105, USA.
J Biol Chem. 1995 Oct 20;270(42):24805-9. doi: 10.1074/jbc.270.42.24805.
The in vivo activity of glutamate dehydrogenase (GDH) in the direction of reductive amination was measured in rat brain at steady-state concentrations of brain ammonia and glutamate after intravenous infusion of the substrate 15NH4+. The in vivo rate was determined from the steady-state fractional 15N enrichment of brain ammonia, measured by selective observation of 15NH4+ protons in brain extract by 1H-15N heteronuclear multiple-quantum coherence transfer NMR, and the rate of increase of brain [15N]glutamate and [2-15N]glutamine measured by 15N NMR. The in vivo GDH activity was 0.76-1.17 mumol/h/g, and 1.1-1.2 mumol/h/g at 1.0 +/- 0.17 mumol/g. Comparison of the observed in vivo GDH activity with the in vivo rates of glutamine synthesis and of phosphate-activated glutaminase suggests that, under mild hyperammonemia, GDH-catalyzed de novo synthesis can provide a minimum of 19% of the glutamate pool that is recycled from neurons to astrocytes through the glutamate-glutamine cycle.
在静脉注射底物15NH4+后，在脑氨和谷氨酸的稳态浓度下，测定了大鼠脑内谷氨酸脱氢酶（GDH）在还原胺化方向上的体内活性。通过1H-15N异核多量子相干转移核磁共振选择性观察脑提取物中的15NH4+质子来测量脑氨的稳态分数15N富集，并通过15N核磁共振测量脑[15N]谷氨酸和[2-15N]谷氨酰胺的增加速率，从而确定体内速率。体内GDH活性为0.76 - 1.17 μmol/h/g，在1.0±0.17 μmol/g时为1.1 - 1.2 μmol/h/g。将观察到的体内GDH活性与谷氨酰胺合成和磷酸激活谷氨酰胺酶的体内速率进行比较表明，在轻度高氨血症下，GDH催化的从头合成可以提供至少19%的谷氨酸池，该谷氨酸池通过谷氨酸-谷氨酰胺循环从神经元再循环到星形胶质细胞。
