分离的豚鼠肾皮质肾小管中谷氨酸碳和氮的去向。谷氨酸脱氢酶参与谷氨酸合成谷氨酰胺的证据。

Fate of glutamate carbon and nitrogen in isolated guinea-pig kidney-cortex tubules. Evidence for involvement of glutamate dehydrogenase in glutamine sythesis from glutamate.

作者信息

Baverel G, Genoux C, Forissier M, Pellet M

出版信息

Biochem J. 1980 Jun 15;188(3):873-80. doi: 10.1042/bj1880873.

DOI:10.1042/bj1880873

PMID:7470041

原文链接:https://pmc.ncbi.nlm.nih.gov/articles/PMC1161972/

Abstract

The pathways and the fate of glutamate carbon and nitrogen were investigated in isolated guinea-pig kidney-cortex tubules. 2. At low glutamate concentration (1 mM), the glutamate carbon skeleton was either completely oxidized or converted into glutamine. At high glutamate concentration (5 mM), glucose, lactate and alanine were additional products of glutamate metabolism. 3. At neither concentration of glutamate was there accumulation of ammonia. 4. Nitrogen-balance calculations and the release of 14CO2 from L-[1-14C]glutamate (which gives an estimation of the flux of glutamate carbon skeleton through alpha-oxoglutarate dehydrogenase) clearly indicated that, despite the absence of ammonia accumulation, glutamate metabolism was initiated by the action of glutamate dehydrogenase and not by transamination reactions as suggested by Klahr, Schoolwerth & Bourgoignie [(1972) Am. J. Physiol. 222, 813-820] and Preuss [(1972) Am. J. Physiol. 222, 1395-1397]. Additional evidence for this was obtained by the use of (i) amino-oxyacetate, an inhibitor of transaminases, which did not decrease glutamate removal, or (ii) L-methionine DL-sulphoximine, an inhibitor of glutamine synthetase, which caused an accumulation of ammonia from glutamate. 5. Addition of NH4Cl plus glutamate caused an increase in both glutamate removal and glutamine synthesis, demonstrating that the supply of ammonia via glutamate dehydrogenase is the rate-limiting step in glutamine formation from glutamate. NH4Cl also inhibited the flux of glutamate through glutamate dehydrogenase and the formation of glucose, alanine and lactate. 6. The activities of enzymes possibly involved in the glutamate conversion into pyruvate were measured in guinea-pig renal cortex. 7. Renal arteriovenous-difference measurements revealed that in vivo the guinea-pig kidney adds glutamine and alanine to the circulating blood.

摘要

在分离的豚鼠肾皮质肾小管中研究了谷氨酸碳和氮的代谢途径及命运。2. 在低谷氨酸浓度（1 mM）时，谷氨酸碳骨架要么完全氧化，要么转化为谷氨酰胺。在高谷氨酸浓度（5 mM）时，葡萄糖、乳酸和丙氨酸是谷氨酸代谢的额外产物。3. 在两种谷氨酸浓度下均未出现氨的积累。4. 氮平衡计算以及L-[1-¹⁴C]谷氨酸释放¹⁴CO₂（可估算谷氨酸碳骨架通过α-酮戊二酸脱氢酶的通量）清楚地表明，尽管没有氨的积累，但谷氨酸代谢是由谷氨酸脱氢酶的作用启动的，而不是如Klahr、Schoolwerth和Bourgoignie [（1972年）《美国生理学杂志》222卷，813 - 820页] 以及Preuss [（1972年）《美国生理学杂志》222卷，1395 - 1397页] 所认为的通过转氨反应启动。通过使用（i）氨基氧乙酸（一种转氨酶抑制剂，它不会降低谷氨酸的清除率）或（ii）L-蛋氨酸DL-亚砜胺（一种谷氨酰胺合成酶抑制剂，它会导致谷氨酸产生氨的积累）获得了这方面的额外证据。5. 添加氯化铵加谷氨酸会导致谷氨酸清除率和谷氨酰胺合成均增加，表明通过谷氨酸脱氢酶供应氨是谷氨酸形成谷氨酰胺的限速步骤。氯化铵还抑制了谷氨酸通过谷氨酸脱氢酶的通量以及葡萄糖、丙氨酸和乳酸的形成。6. 在豚鼠肾皮质中测量了可能参与谷氨酸转化为丙酮酸的酶的活性。7. 肾动静脉差异测量显示，在体内豚鼠肾脏会向循环血液中添加谷氨酰胺和丙氨酸。