Mitochondrial and cytosolic alanine aminotransferases (EC 2.6.1.2) were partially purified (140- and 180-fold), respectively) from bovine brain cortex by means of (NH4)2SO4 precipitation, gel filtration on Sephadex G-150, and in-exchange chromatography on DEAE A-50 and characterized. The enzymes exhibited identical molecular weights (110,000 +/- 10,000) and pH optima (7.8), but were eluted from CM Sephadex C-50 at different ionic strengths. Isoelectric focusing of the enzymes indicated a pI value of 5.2 for the cytosolic enzyme and 7.2 for the mitochondrial enzyme. The Km values of the mitochondrial enzyme were 5.1 mM, 6.6 mM, 0.7 mM, and 0.4 mM and of the cytosolic isozyme were 30.3 mM, 4.3 mM, 0.7 mM, and 0.5 mM for alanine, glutamate, 2-oxoglutarate, and pyruvate, respectively. The results indicated that two forms of alanine aminotransferase exist in nerve tissue, which suggests that they may play different roles in the cellular metabolism of nerve tissue.

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Abstract— Alanine aminotransferase activity in subcellular fractions of rat brains was investigated during ontogenic development. The activity rose from the prenatal period until adulthood, the highest increase being observed during the period of morphological metabolic and functional maturation of the brain. The rise of the total activity was due predominantly to a rise in the activity of the cytosblic enzyme; the activity of the mitochondrial enzyme did not change markedly during ontogeny. CI‐ions and elevated temperature (55°C) inhibited the activity only of the mitochondrial enzyme. Raised temperature stimulated the activity of the cytosolic enzyme while CI‐ions did not influence its activity. Our results indicate that 2 alanine aminotransferase isoenzlmes are already present in the rat brain in the prenatal period. It is assumed that the cytosolic enzyme is involved in the regulation of tissue glycol)sis and alanine formation, while the mitochondrial enzyme plays a role in the amino nitrogen transport between mitochondria and cytosol.

SUMMARY1. Slices of brain cortex from rabbits were incubated in Ringer solution and in Ringer modified by the removal of calcium and sodium, and the addition of ouabain, oligomycin or extra potassium. The potassium content of the tissue, the oxygen consumption and the lactate production from glucose were measured and found to be interrelated.2. Incubation in high-K Ringer caused an increase in oxygen consumption that was prevented by ouabain, oligomycin and deprivation of sodium. Lactate production was also raised, but this increase was unaffected by ouabain and raised further by oligomycin.3. Calcium omission raised metabolism; the tissue K content was unaffected. Oligomycin always decreased oxygen consumption and raised lactate production further. The metabolic responses to calcium, potassium, ouabain and oligomycin depended on sodium.4. After anaerobic incubation, the tissue potassium concentration was still 5 times higher than that in Ringer. It was unaffected by oligomycin but lowered markedly by ouabain.5. The synergistic effects of sodium with potassium, oligomycin, calcium, and calcium plus ouabain suggest that the metabolic responses of brain cortex slices to a high-K Ringer depend on the operation of the sodium pump.