REGIONAL AND SUBCELLULAR DISTRIBUTION OF AMINOTRANSFERASES IN RAT BRAIN

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Abstract
Abstract— Aminotransferase activity was measured in various areas of the nervous system of the rat (cortical grey matter, midbrain, corpus callosum, spinal cord and sciatic nerve) and in subcellular fractions of rat brain (nuclei, mitochondria and cytosol). Activity was low or absent in the sciatic nerve relative to that in the other areas, with the exception of incubation of glutamate with oxaloacetate (25 per cent of the activity found in brain) and of asparagine with 2‐oxoglutarate (65 per cent of the activity found in brain). The distribution of enzymic activity was not homogeneous; alanine‐2‐oxoglutarate aminotransferase was highest in cortical grey matter; leucine‐ and GABA‐2‐oxoglutarate aminotransferases were highest in midbrain. Incubation of phenylalanine or tyrosine with 2‐oxoglutarate gave similar activities in grey matter and midbrain. Activity generally was higher in the grey matter than in corpus callosum or spinal cord. However, incubations of methionine with 2‐oxoglutarate, or glutamine with glyoxylate, gave similar activities in the three areas studied from the brain, whereas incubations of glutamate with glyoxylate gave highest activity in the corpus callosum. Only incubations of asparagine with 2‐oxoglutarate, and glutamate with glyoxylate, gave significant activity in the nuclear subcellular fraction. Aminotransferase activity of phenylalanine, tyrosine or GABA with 2‐oxoglutarate, or ornithine or glutamine with glyoxylate, was localized to mitochondria. The remaining reactions studied (glutamate with oxaloacetate; leucine, alanine, methionine or asparagine with 2‐oxoglutarate and glutamate with glyoxylate) demonstrated activity in both the mitochondrial fraction and the soluble supernatant fraction.