Journal
NEUROCHEMISTRY INTERNATIONAL
Volume 37, Issue 2-3, Pages 229-241Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/S0197-0186(00)00042-5
Keywords
glutamate; glutamine; synaptic terminals; synaptosomes; energy metabolism; compartmentation; glutamate dehydrogenase; aspartate aminotransferase; neurons; astrocytes
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Funding
- NICHD NIH HHS [HD16596] Funding Source: Medline
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There have been numerous studies on the activity and localization of aspartate aminotransferase (AAT) and glutamate dehydrogenase (GDH) in brain tissue. However, there is still a controversy as to the specific roles and relative importance of these enzymes in glutamate and glutamine metabolism in astrocytes and neurons or synaptic terminals. There are many reports documenting GDH activity in synaptic terminals, yet the misconception that it is a glial enzyme persists. Furthermore, there is evidence that this tightly regulated enzyme may have an increased role in synaptic metabolism in adverse conditions such as low glucose and hyperammonemia that could compromise synaptic function. In the present study, we report high activity of both AAT and GDH in mitochondrial subfractions from cortical synaptic terminals. The relative amount of GDH/AAT activity was higher in SM2 mitochondria, compared to SMI mitochondria. Such a differential distribution of enzymes can contribute significantly to the compartmentation of metabolism. There is evidence that the metabolic capabilities of the SMI and SM2 subfractions of synaptic mitochondria are compatible with the compartments A and B of neuronal metabolism proposed by Waagepetersen et al. (1998b. Dev. Neurosci. 20, 310-320). (C) 2000 Elsevier Science Ltd. All rights reserved.
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