Tannen R L, Kunin A S
Kidney Int. 1982 Sep;22(3):280-5. doi: 10.1038/ki.1982.166.
The effect of the tricarboxylic acid (TCA) cycle precursor, pyruvate, on glutamine metabolism by isolated renal cortical mitochondria was assessed by quantitating its key nitrogen and carbon metabolites. When mitochondria from normal rats were incubated at pH 7.4, pyruvate (2 mM) inhibited ammonia production by almost completely erradicating glutamate deamination and by diminishing glutamine deamidation but to a lesser extent. Alpha KG, citrate, and malate accumulation in the incubation medium were increased dramatically reflecting the increased flux of pyruvate through the TCA cycle; the intramitochondrial concentrations of both Alpha KG and glutamate were increased. Thus, pyruvate primarily inhibits flux through glutamate dehydrogenase as a result either of an increase in Alpha KG concentration and/or a decrease in the redox (NAD/NADH) potential secondary to enhanced flux through the TCA cycle. Glutamine deamidation is secondarily inhibited, presumably due to the increased intramitochondrial concentration of glutamate. Citrate (2 mM) produced changes comparable to those observed with pyruvate. Mitochondria from normal rats incubated at pH 7.0 as well as mitochondria from rats with chronic metabolic acidosis responded to pyruvate in a fashion qualitatively similar to normal mitochondria incubated at pH 7.4. Glutamate deamination was inhibited significantly, but a high rate persisted with chronic acidosis despite the presence of pyruvate. Nevertheless, when glutamine metabolism was contrasted with normal mitochondria incubated at pH 7.4, the response to in vitro incubation in an acid pH as well as to chronic metabolic acidosis was similar quantitatively regardless of whether glutamine alone or in combination with pyruvate was present in the incubation medium.
通过定量关键的氮和碳代谢产物，评估了三羧酸（TCA）循环前体丙酮酸对分离的肾皮质线粒体谷氨酰胺代谢的影响。当将正常大鼠的线粒体在pH 7.4下孵育时，丙酮酸（2 mM）通过几乎完全消除谷氨酸脱氨作用以及减少谷氨酰胺脱酰胺作用（但程度较小）来抑制氨的产生。孵育培养基中α-酮戊二酸、柠檬酸和苹果酸的积累显著增加，这反映了丙酮酸通过TCA循环的通量增加；线粒体内α-酮戊二酸和谷氨酸的浓度均升高。因此，丙酮酸主要通过α-酮戊二酸浓度的增加和/或由于通过TCA循环通量增强导致的氧化还原（NAD/NADH）电位降低，来抑制谷氨酸脱氢酶的通量。谷氨酰胺脱酰胺作用继而受到抑制，推测是由于线粒体内谷氨酸浓度增加所致。柠檬酸（2 mM）产生的变化与丙酮酸观察到的变化相当。在pH 7.0下孵育的正常大鼠的线粒体以及患有慢性代谢性酸中毒大鼠的线粒体，对丙酮酸的反应在质量上与在pH 7.4下孵育的正常线粒体相似。谷氨酸脱氨作用受到显著抑制，但尽管存在丙酮酸，慢性酸中毒时仍维持较高的速率。然而，当将谷氨酰胺代谢与在pH 7.4下孵育的正常线粒体进行对比时，无论孵育培养基中单独存在谷氨酰胺还是与丙酮酸一起存在，对酸性pH下的体外孵育以及慢性代谢性酸中毒的反应在数量上都是相似的。
