Alanine aminotransferase in bovine brain: purification and properties

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.