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首页> 外文期刊>American Journal of Physiology >Aspartate aminotransferase isotope exchange reactions: implications for glutamate/glutamine shuttle hypothesis.
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Aspartate aminotransferase isotope exchange reactions: implications for glutamate/glutamine shuttle hypothesis.

机译：天冬氨酸氨基转移酶同位素交换反应：对谷氨酸/谷氨酰胺穿梭假设的影响。

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摘要

Aspartate aminotransferase (AAT) catalyzes amino group transfer from glutamate (Glu) or aspartate (Asp) to a keto acid acceptor-oxaloacetate (OA) or alpha-ketoglutarate (KG), respectively. Data presented here show that AAT catalyzes two partial reactions resulting in isotope exchange between 3H-labeled Glu or 3H-labeled Asp and the cognate keto acid in the absence of the keto acid acceptor required for the net reaction. Tritiated keto acid product was detected by release of 3H2O from C-3 during base-induced enolization. Tritium released directly from C-2 (or C-3) by the enzyme was also evaluated and is a small fraction of that released because of exchange to the keto acid pool. Exchange is dependent on AAT concentration, time-dependent, proportional to the amino-to-keto acid ratio, and blocked by aminooxyacetate (AOA), an AAT inhibitor. Enzymatic conversion of [3H]KG to Glu by glutamic dehydrogenase (GDH) or of [3H]OA to malate by malic dehydrogenase (MDH) "protects" the label from release by base, showing that base-induced isotope release is from keto acid rather than a result of release during the exchange process. AAT isotope exchange is discussed in the context of the glutamate/glutamine shuttle hypothesis for astrocyteeuron carbon cycling.
机译：天冬氨酸氨基转移酶（AAT）分别催化从谷氨酸（Glu）或天冬氨酸（Asp）到酮酸受体草酰乙酸酯（OA）或α-酮戊二酸酯（KG）的氨基转移。此处提供的数据表明，AAT催化两个部分反应，导致3H标记的Glu或3H标记的Asp与同源酮酸之间发生同位素交换，而没有净反应所需的酮酸受体。通过在碱诱导的烯醇化过程中从C-3释放3H2O来检测化的酮酸产物。还评估了由酶直接从C-2（或C-3）释放的，由于与酮酸库的交换，的释放量很小。交换取决于AAT浓度，时间依赖性，与氨基与酮酸之比成比例，并被AAT抑制剂氨基氧乙酸酯（AOA）阻断。谷氨酸脱氢酶（GDH）将[3H] KG酶转化为Glu或苹果酸脱氢酶（MDH）将[3H] OA转化为苹果酸“保护”标签不受碱基释放，表明碱基诱导的同位素释放来自酮酸而不是在交换过程中释放的结果。在星形胶质细胞/神经元碳循环的谷氨酸/谷氨酰胺穿梭假设的背景下讨论了AAT同位素交换。

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