Cheeseman A J, Clark J B
Department of Biochemistry, Medical College, St. Bartholomew's Hospital, University of London, England.
J Neurochem. 1988 May;50(5):1559-65. doi: 10.1111/j.1471-4159.1988.tb03044.x.
beta-Methyleneaspartate, a specific inhibitor of aspartate aminotransferase (EC 2.6.1.1.), was used to investigate the role of the malate-aspartate shuttle in rat brain synaptosomes. Incubation of rat brain cytosol, "free" mitochondria, synaptosol, and synaptic mitochondria, with 2 mM beta-methyleneaspartate resulted in inhibition of aspartate aminotransferase by 69%, 67%, 49%, and 76%, respectively. The reconstituted malate-aspartate shuttle of "free" brain mitochondria was inhibited by a similar degree (53%). As a consequence of the inhibition of the aspartate aminotransferase, and hence the malate-aspartate shuttle, the following changes were observed in synaptosomes: decreased glucose oxidation via the pyruvate dehydrogenase reaction and the tricarboxylic acid cycle; decreased acetylcholine synthesis; and an increase in the cytosolic redox state, as measured by the lactate/pyruvate ratio. The main reason for these changes can be attributed to decreased carbon flow through the tricarboxylic acid cycle (i.e., decreased formation of oxaloacetate), rather than as a direct consequence of changes in the NAD+/NADH ratio. Malate/glutamate oxidation in "free" mitochondria was also decreased in the presence of 2 mM beta-methyleneaspartate. This is probably a result of decreased glutamate transport into mitochondria as a result of low levels of aspartate, which are needed for the exchange with glutamate by the energy-dependent glutamate-aspartate translocator.
β-亚甲基天冬氨酸是天冬氨酸转氨酶（EC 2.6.1.1.）的一种特异性抑制剂，被用于研究苹果酸-天冬氨酸穿梭在大鼠脑突触体中的作用。用2 mM β-亚甲基天冬氨酸孵育大鼠脑胞质溶胶、“游离”线粒体、突触溶胶和突触线粒体，分别导致天冬氨酸转氨酶活性被抑制69%、67%、49%和76%。“游离”脑线粒体中重构的苹果酸-天冬氨酸穿梭也受到类似程度的抑制（53%）。由于天冬氨酸转氨酶受到抑制，进而苹果酸-天冬氨酸穿梭也受到抑制，在突触体中观察到以下变化：通过丙酮酸脱氢酶反应和三羧酸循环的葡萄糖氧化减少；乙酰胆碱合成减少；以及通过乳酸/丙酮酸比值测定的胞质氧化还原状态增加。这些变化的主要原因可归因于通过三羧酸循环的碳流量减少（即草酰乙酸形成减少），而非NAD⁺/NADH比值变化的直接结果。在存在2 mM β-亚甲基天冬氨酸的情况下，“游离”线粒体中的苹果酸/谷氨酸氧化也减少。这可能是由于天冬氨酸水平较低导致谷氨酸转运进入线粒体减少的结果，而天冬氨酸是通过能量依赖的谷氨酸-天冬氨酸转运体与谷氨酸交换所必需的。
