Meijer A J, Van Woerkom G M, Wanders R J, Lof C
Eur J Biochem. 1982 May 17;124(2):325-30. doi: 10.1111/j.1432-1033.1982.tb06595.x.
The permeability properties of the rat-liver mitochondrial membrane for N-acetylglutamate, the activator of carbamoyl-phosphate synthetase (ammonia), were studied. 1. Transport of N-acetylglutamate into the mitochondria was only observed in partially or fully de-energized mitochondria and when the extramitochondrial concentration was unphysiologically high (in the mM range). However, even under these conditions the intramitochondrial concentration of N-acetylglutamate was much lower than that outside. 2. Mitochondrial N-acetylglutamate efflux only occurs when the mitochondria are in an energized state. At 25 degrees C, at an intramitochondrial N-acetylglutamate concentration of 0.7-1.0 nmol/mg protein, efflux proceeds at a rate of about 0.05 nmol X min-1 X mg protein-1. This is 10-fold lower than the maximal rate of N-acetylglutamate synthesis in the mitochondria. 3. Homologous exchange between intramitochondrial N-[14C]acetylglutamate and extramitochondrial unlabelled N-acetylglutamate could not be demonstrated. 4. It is concluded that transport of N-acetylglutamate in vivo is effectively unidirectional, out of the mitochondria. This behaviour is in accordance with the physiological requirement for efflux of N-acetylglutamate from the mitochondria in order to be degraded in the cytosol.
对大鼠肝脏线粒体膜对氨甲酰磷酸合成酶（氨）的激活剂N-乙酰谷氨酸的通透性进行了研究。1. 仅在部分或完全去能的线粒体中，且线粒体外浓度处于非生理高值（毫摩尔范围）时，才观察到N-乙酰谷氨酸向线粒体的转运。然而，即使在这些条件下，线粒体内N-乙酰谷氨酸的浓度也远低于外部浓度。2. 线粒体N-乙酰谷氨酸外流仅在线粒体处于能化状态时发生。在25℃下，当线粒体内N-乙酰谷氨酸浓度为0.7 - 1.0 nmol/mg蛋白质时，外流速率约为0.05 nmol·min⁻¹·mg蛋白质⁻¹。这比线粒体中N-乙酰谷氨酸合成的最大速率低10倍。3. 未证明线粒体内N-[¹⁴C]乙酰谷氨酸与线粒体外未标记的N-乙酰谷氨酸之间的同源交换。4. 得出结论，体内N-乙酰谷氨酸的转运实际上是单向的，从线粒体流出。这种行为符合N-乙酰谷氨酸从线粒体流出以便在细胞质中降解的生理需求。
