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Investigation of the penetration of oxaloacetate into rat liver mitochondria 1. 1. The penetration of oxaloacetate into rat liver mitochondria was estimated by fluorimetric measurement of the redox change of intramitochondrial pyridine nucleotides after addition of oxaloacetate. The initial change in fluorescence was proportional to NADH oxidation, as demonstrated by quantitative analysis of pyridine nucleotides. 2. 2. The penetration was stimulated maximally by 1 mM Ca 2+ . Mg 2+ also stimulated penetration but to a lesser degree. K + (+ valinomycin) was without effect. Ca 2+ had a stimulating effect also after preincubation with 4,5,6,7-tetrachloro-2-trifluoromethylbenzimidazol (TTFB). 3. 3. The penetration was almost completely inhibited by TTFB in a time-dependent process with a halflife at 0.5 min. In the presence of serum albumin the penetration was reactivated up to 80%. ATP caused acceleration of reactivation. 4. 4. ATP alone inhibited the penetration in a competitive manner to the same degree as AMP. Higher concentrations of KCl also showed a competitive inhibition. 5. 5. It is suggested that oxaloacetate is exchanged with endogenous anions, and the inhibition by TTFB is caused by loss of endogenous anions. 6. 6. Because of the strong competitive inhibition by anions, the penetration of oxaloacetate seems to be of limited importance in vivo .

1. 1. The energy-independent exchange of alkali metal cations against protons was investigated in intact and disintegrated mitochondria. The exchange is not specific for different alkali metal ions. 2. 2. In intact mitochondria the apparent Km for the energy-independent exchange range from 5 to 25 mM (Cs+, Rb+, K+ 5–10 mM; Na+ 15 mM; Li+ 20 mM). At all ions studied the maximum release of protons was 15–20 nval/mg protein. 3. 3. In disintegrated mitochondria there are no differences between the alkali metal ions (apparent Km 30 mM; maximum H+-release 50 nval/mg protein). 4. 4. Directly accessible binding sites seem to exist in the outer membrane. Binding sites in the inner membrane are accessible only after disintegration, but not after addition of valinomycin + rotenone.

ZusammenfassungDisentegration oder Alterung führt bei intakten Lebermitochondrien und bei der Innenmembrant + Matrix-Fraktion (Digitonin) zu einer Zunahme der K+-bedingten Protonenfreisetzung, nicht jedoch bei Aussenmembranen. Es wird geschlossen, dass auch die Innenmembran + Matrix-Fraktion Austauschstallen für K+ enthält, die jedoch bei struktureller Integrität nicht frei zugänglich sind. Die dem intermembrane space zugewandte Seite der Innenmembran stellt möglicherweise eine Barriere für das K+-Ion dar.AbstractDisintegration or altering of intact mitochondria or digitonin inner membrane + matrix particles causes an increase in K+-linked release of protons. This effect is not obtainable in the case of outer membranes. It is assumed, that also the inner membrane + matrix possesses exchange sites for K+, which are freely accessible for the potassium ion if the structural integrity is damaged. The outer layer of inner membrane seems to be a barrier for the K+-movement.