Ross C D, Godfrey D A
J Histochem Cytochem. 1985 Jul;33(7):624-30. doi: 10.1177/33.7.4008916.
Aspartate aminotransferase (AAT), an enzyme interconverting glutamate and aspartate, has been suggested to be a marker for glutamatergic and/or aspartatergic neurons. However, AAT, glutamate, and aspartate are also involved in cellular metabolism, e.g., the malate-aspartate shuttle. To investigate the extent to which AAT might be involved in these several functions in retina, the distribution of AAT activity in rat retinal layers was compared to that of malate dehydrogenase (MDH), an enzyme of aerobic metabolism proposed to be physically complexed with AAT in the malate-aspartate shuttle mechanism. The distribution of AAT activity in retinal layers closely paralleled that of MDH (correlation coefficient AAT versus MDH = 0.93). AAT activity was proportionately higher than MDH in the photoreceptor inner segments, containing a high density of mitochondria, and in the outer plexiform layer (OPL), containing photoreceptor terminals and bipolar and horizontal cell processes. The amount of total AAT activity in the inner segments related to the mitochondrial isoenzyme is almost twice that in the other layers tested, including the OPL. The correlation between AAT and MDH activities is consistent with AAT involvement in retinal energy metabolism, although other functions, such as neurotransmission, are possible.
天冬氨酸转氨酶（AAT）是一种可使谷氨酸和天冬氨酸相互转化的酶，有人认为它是谷氨酸能和/或天冬氨酸能神经元的标志物。然而，AAT、谷氨酸和天冬氨酸也参与细胞代谢，例如苹果酸-天冬氨酸穿梭。为了研究AAT在视网膜中参与这些功能的程度，将大鼠视网膜各层中AAT活性的分布与苹果酸脱氢酶（MDH）的分布进行了比较，MDH是有氧代谢中的一种酶，在苹果酸-天冬氨酸穿梭机制中被认为与AAT在物理上形成复合物。视网膜各层中AAT活性的分布与MDH的分布密切平行（AAT与MDH的相关系数=0.93）。在含有高密度线粒体的光感受器内节以及含有光感受器终末、双极细胞和水平细胞突起的外网状层（OPL）中，AAT活性比MDH相应地更高。内节中与线粒体同工酶相关的总AAT活性几乎是包括OPL在内的其他测试层的两倍。AAT和MDH活性之间的相关性与AAT参与视网膜能量代谢一致，尽管也可能有其他功能，如神经传递。
