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Metabolism of [C-14] glutamate and [C-14] glutamine by the ectomycorrhizal fungus Paxillus involutus

机译:外生菌根真菌paxillus involutus对[C-14]谷氨酸和[C-14]谷氨酰胺的代谢

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摘要

To examine pathways of glutamate and glutamine metabolism in the ectomycorrhizal fungus Paxillus involutus, tracer kinetic experiments were performed using L-[U-C-14]glutamate and L-[U-C-14]glutamine and the enzyme inhibitors methionine sulfoximine (MSX), azaserine (AZA) and aminooxyacetate (AOA). When [C-14]glutamate was supplied to fungal cultures, 25% of the radioactivity of the amino acid fraction was incorporated into glutamine after 5 min feeding, but MSX inhibited incorporation of C-14 into glutamine by 85%, suggesting the rapid operation of glutamine synthetase. Conversely, when P. involutus was fed with [C-14]glutamine, 46% of the label was found in glutamate within 30 min of feeding and AZA inhibited glutamate formation by 90%. Taken together, these data indicate that glutamate synthase (GOGAT) is the major enzyme of glutamine degradation. In addition, the strong inhibition of glutamine utilization by AOA indicates that glutamine catabolism in P. involutus might involve a transamination process as an alternative pathway to GOCAT for glutamine degradation. The high (CO2)-C-14 evolution shows that glutamate and glutamine are further actively consumed as respiratory substrates, being channelled through the tricarboxylic acid (TCA) cycle and oxidized as CO2. It appears that synthesis of amino acid precursors during TCA cycle operation is an essential step far aspartate and alanine synthesis through aminotransferase activities in P. involutus.
机译:为了检查外生菌根真菌Paxillus involutus中的谷氨酸和谷氨酰胺代谢途径,使用L- [UC-14]谷氨酸和L- [UC-14]谷氨酰胺以及酶抑制剂蛋氨酸硫代亚胺(MSX),氮杂黄嘌呤( AZA)和氨基氧乙酸盐(AOA)。当将[C-14]谷氨酸提供给真菌培养物时,进食5分钟后25%氨基酸的放射性被掺入了谷氨酰胺中,但MSX抑制了C-14掺入谷氨酰胺中的比例为85%,表明该操作迅速谷氨酰胺合成酶。相反地​​,当用[C-14]谷氨酰胺饲喂对渐密线虫时,在饲喂30分钟内在谷氨酸中发现46%的标记,而AZA则抑制了90%的谷氨酸形成。综上所述,这些数据表明谷氨酸合酶(GOGAT)是谷氨酰胺降解的主要酶。此外,AOA对谷氨酰胺利用的强烈抑制作用表明,渐隐线虫中的谷氨酰胺分解代谢可能涉及转氨过程,作为GOCAT谷氨酰胺降解的替代途径。 (CO2)-C-14的高度释放表明,谷氨酸和谷氨酰胺被呼吸道底物进一步活跃地消耗,通过三羧酸(TCA)循环被引导并被氧化为CO2。似乎在TCA循环操作过程中氨基酸前体的合成是重要的步骤,这是通过渐开线虫中的氨基转移酶活性来合成天冬氨酸和丙氨酸所必需的。

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