Abstract
1. 1. Addition of ammonia inhibits oxygen uptake in phosphorylating rat-liver mitochondria when α-ketoglutarate or pyruvate is used as substrate. 2. 2. When α-ketoglutarate is used there is an approximately stoichiometric relation between the depression in oxygen uptake and the amount of ammonia incorporated into amino acid: Δ 1 2 O 2 ≅ Δ NH 4 + ≅ Δ α- NH 2 3. 3. The maximum inhibition of oxygen uptake observed under the reported experimental conditions is about 40%. Half-maximal inhibition is obtained with ammonia concentration of 7 · 10 −3 M. 4. 4. Ammonia does not inhibit oxygen uptake in mitochondria respiring in the absence of phosphate acceptor. 5. 5. As an explanation of these results, a competition for DPNH between glutamic dehydrogenase and the electron-transport chain is suggested.
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