Regional and subcellular distribution of enzymes of branched-chain amino acid metabolism in brains of normal and diabetic rats.
Branched-chain-amino-acid:alpha-ketoglutarate transaminase and branched-chain alpha-ketoacid dehydrogenase have been assayed in brains of control and of streptozotocin-induced diabetic rats. Enzyme activities were measured in five distinct regions of the brain: cerebellum, pons + medulla, midbrain, thalamus + hypothalamus, and telencephalon. Subcellular distribution of these enzymes in whole brain was assessed by fractionating brain homogenate into cytoplasm, free mitochondria, and synaptosomes. The following enzymes were used as markers: lactate dehydrogenase for cytoplasm, glutamate dehydrogenase for mitochondria, and glutamate decarboxylase for synaptosomes. The activity of the branched-chain amino acid transaminase in all brain regions was considerably higher than that of the branched-chain alpha-ketoacid dehydrogenase. While the highest activity of the transaminase occurred in brain-stem regions, the highest activity of the dehydrogenase was present in cerebellum and telencephalon. Diabetes did not affect the activity of the transaminase, but it caused a decrease in the total activity of the dehydrogenase in midbrain and in thalamus + hypothalamus. The transaminase was localized in the cytoplasmic fraction of whole brain, while the dehydrogenase was enriched in the free mitochondria.
D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide); D000597:Amino Acids, Branched-Chain / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000201:enzymology*; D003593:Cytoplasm / Q000201:enzymology; D003921:Diabetes Mellitus, Experimental / Q000201:enzymology*; D007658:Ketone Oxidoreductases / Q000378:metabolism; D008297:Male; D008928:Mitochondria / Q000201:enzymology; D009097:Multienzyme Complexes / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013347:Subcellular Fractions / Q000201:enzymology*; D013574:Synaptosomes / Q000201:enzymology; D000637:Transaminases / Q000378:metabolism
D000597:Amino Acids, Branched-Chain; D009097:Multienzyme Complexes; D007658:Ketone Oxidoreductases; D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide); D000637:Transaminases; C019798:branched-chain-amino-acid transaminase