Glutamate dehydrogenase activation and ammonia formation by rat kidney mitochondria.
Glutamate dehydrogenase activation and ammonia formation by rat kidney mitochondria.
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大鼠肾线粒体谷氨酸脱氢酶激活和氨形成。
DOI：
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发表时间：
1978
影响因子：
4.8
通讯作者：
K. Lanoue
中科院分区：
文献类型：
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作者：
A. Schoolwerth;B. Nazar;K. Lanoue
将大鼠肾皮质的线粒体与生理浓度的谷氨酸或谷氨酰胺或两者一起孵育。在介质中的氨，谷氨酸，谷氨酰胺和天冬氨酸的变化进行了测量，并通过谷氨酸脱氢酶，转氨酶，谷氨酸-乙酸转氨酶通量计算在不同的pH值水平在体外和动物的线粒体中，其中代谢性酸中毒在体内诱导。在单独的谷氨酸作为底物的存在下，天冬氨酸形成总是相对于氨形成大。将pH值从7.4降低到6.8会减少天冬氨酸的产生，但不会导致氨形成的持续增加。在pH 7.4的脱氨途径占21%，在pH 6.8，26%的总谷氨酸利用。当谷氨酰胺是唯一的底物和谷氨酸在线粒体内产生时，脱氨途径在pH 7.4和pH 6.8下分别占谷氨酸利用率的39%和32%。在pH 7.4时，通过谷氨酰胺酶、谷氨酸脱氢酶和谷氨酸-乙酸转氨酶的通量均高于在pH 6.8时测得的通量。以谷氨酰胺和谷氨酸为底物，谷氨酸代谢几乎完全通过转氨作用发生，脱氨途径可以忽略不计。在两种底物的存在下，由从经历7天NH 4Cl酸中毒的动物分离的线粒体产生的氨增加235%。谷氨酸脱氨显着加速，并贡献了一半的增强氨合成。以谷氨酰胺为底物，谷氨酸脱氢酶通量增加4倍，而谷氨酰胺酶通量增加a倍。在谷氨酰胺和谷氨酸的存在下，谷氨酸脱氢酶通量的增加甚至更加显著，与对照相比上升了50倍。谷氨酸脱氢酶通量的增加不能完全解释为谷氨酸脱氢酶活性的增加、谷氨酸转运的增强、线粒体氧化还原状态的改变或平衡代谢的改变。
Mitochondria from rat renal cortex were incubated with physiological concentrations of glutamate, or glutamine, or both. Changes in medium ammonia, glutamate, glutamine, and aspartate were measured and fluxes through glutamate dehydrogenase, glutaminase, and glutamate oxalacetate transaminase were calculated at different pH levels in vitro and in mitochondria from animals in which metabolic acidosis was induced in vivo. In the presence of glutamate alone as substrate, aspartate formation was always large with respect to ammonia formation. Lowering the pH from 7.4 to 6.8 decreased aspartate production but resulted in no consistent increase in ammonia formation. At pH 7.4 the deamination pathway accounted for 21% and, at pH 6.8, 26% of the total glutamate utilization. When glutamine was the only substrate and glutamate was generated inside the mitochondria, the deamination pathway accounted for 39% of the glutamate utilization at pH 7.4 and 32% at pH 6.8. At pH 7.4 fluxes through glutaminase, glutamate dehydrogenase, and glutamate oxalacetate transaminase were all high with respect to the fluxes measured at pH 6.8. With both glutamine and glutamate as substrates, glutamate metabolism occurred almost exclusively by transamination and the deamination pathway was negligible. Ammonia generation by mitochondria isolated from animals subjected to 7 days of NH&l acidosis was increased 235% in the presence of both substrates. Glutamate deamination was markedly accelerated and contributed one-half of the augmented ammonia synthesis. With glutamine as substrate, glutamate dehydrogenase flux increased 4-fold while glutaminase flux rose a-fold. In the presence of both glutamine and glutamate, the increase in glutamate dehydrogenase flux was even more marked, rising 50-fold compared to control. The increase in glutamate dehydrogenase flux could not be explained entirely by an increase in glutamate dehydrogenase enzyme activity, enhanced glutamate transport, an alteration in the mitochondrial oxidation-reduction state or by equilibrium considera