The subcellular distribution of rat liver l-alanine–glyoxylate aminotransferase in relation to a pathway for glucose formation involving glyoxylate

1. The distribution of l-alanine–glyoxylate aminotransferase activity between subcellular fractions prepared from rat liver homogenates was investigated. The greater part of the homogenate activity (about 80%) was recovered in the `total-particles' fraction sedimented by high-speed centrifugation and the remainder in the cytosol fraction. 2. Subfractionation of the particles by differential sedimentation and on sucrose density gradients revealed a specific association between the aminotransferase and the mitochondrial enzymes glutamate dehydrogenase and rhodanese. 3. The aminotransferase activities in the cytosol and the mitochondria are due to isoenzymes. The solubilized mitochondrial enzyme has a pH optimum of 8.6, an apparent Km of 0.24mm with respect to glyoxylate and is inhibited by glyoxylate at concentrations above 5mm. The cytosol aminotransferase shows no distinct pH optimum (over the range 7.0–9.0) and has an apparent Km of 1.11mm with respect to glyoxylate; there is no evidence of inhibition by glyoxylate. 4. The mitochondrial location of the bulk of the rat liver l-alanine–glyoxylate aminotransferase activity is discussed in relation to a pathway for gluconeogenesis involving glyoxylate.