Origin of the Ammonia Found in Protein‐Free Extracts of Rat‐Liver Mitochondria and Rat Hepatocytes

Abstract

1. Protein‐free extracts of isolated rat‐liver mitochondria contain 5.17 ± 0.19 nmol ammonia/mg protein [cf. Harris, E. J. and Bassett, D. J. (1971) FEBS Lett. 19, 214–2171. 2. The ammonia found in the protein‐free extracts does not originate from lysosomes contaminating the mitochondrial preparation. 3. When isolated mitochondria are incubated with ornithine, 14CO2 and a source of ATP a small amount of citrulline is formed. This amount is stoichiometrically equivalent to the ammonia that disappears from the extramitochondrial space, whereas the amount of ammonia found in the protein‐free extracts of the mitochondria remains unchanged. Similar results were obtained when the reductive amination of 2‐oxoglutarate was used as an ammonia‐consuming reaction. 4. When isolated mitochondria are incubated under conditions such that the glutamate dehydrogenase and 3‐hydroxybutyrate dehydrogenase reactions reach equilibrium, the thermodynamically active concentration of ammonia is not equal to the concentration measured in the protein‐free extracts. 5. About 80% of the ammonia found in protein‐free extracts of rat‐liver mitochondria is derived from a component or components with a molecular weight of ≧ 50000. 6. Protein‐free extracts of isolated rat‐liver cells contain considerable amounts of ammonia. After digitonin fractionation this ammonia is found in the protein‐free extract of the particulate fraction. 7. It is concluded that the ammonia found in protein‐free extracts of rat‐liver tissue is derived from a component or components in the mitochondria and is released during deproteinization. Copyright © 1980, Wiley Blackwell. All rights reserved