线粒体
呼吸
谷氨酸受体
生物化学
谷氨酸脱氢酶
氧化磷酸化
新陈代谢
丙酮酸脱氢酶复合物
化学
苹果酸脱氢酶
呼吸链
柠檬酸合酶
细胞呼吸
生物
酶
受体
植物
作者
Daniela R. Melo,Sandra R. Mirandola,Nilson Antônio Assunção,Roger F. Castilho
摘要
Abstract The neurodegeneration that occurs in methylmalonic acidemia is proposed to be associated with impairment of mitochondrial oxidative metabolism resulting from methylmalonate (MMA) accumulation. The present study evaluated the effects of MMA on oxygen consumption by isolated rat brain mitochondria in the presence of NADH‐linked substrates (α‐ketoglutarate, citrate, isocitrate, glutamate, malate, and pyruvate). Respiration supported either by glutamate or glutamate plus malate was significantly inhibited by MMA (1–10 mM), whereas no inhibition was observed when a cocktail of NADH‐linked substrates was used. Measurements of glutamate transport revealed that the inhibitory effect of MMA on respiration maintained by this substrate is not due to inhibition of its mitochondrial uptake. In light of this result, the effect of MMA on the activity of relevant enzymes involved in mitochondrial glutamate metabolism was investigated. MMA had minor inhibitory effects on glutamate dehydrogenase and aspartate aminotransferase, whereas α‐ketoglutarate dehydrogenase was significantly inhibited by this metabolite (K i = 3.65 mM). Moreover, measurements of α‐ketoglutarate transport and mitochondrial MMA accumulation indicated that MMA/α‐ketoglutarate exchange depletes mitochondria from this substrate, which may further contribute to the inhibition of glutamate‐sustained respiration. To study the effect of chronic in vivo MMA treatment on mitochondrial function, young rats were intraperitoneally injected with MMA. No significant difference was observed in respiration between isolated brain mitochondria from control and MMA‐treated rats, indicating that in vivo MMA treatment did not lead to permanent mitochondrial respiratory defects. Taken together, these findings indicate that the inhibitory effect of MMA on mitochondrial oxidative metabolism can be ascribed to concurrent inhibition of specific enzymes and lower availability of respiratory substrates. © 2012 Wiley Periodicals, Inc.
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