The Transport of Citric-Acid-Cycle Intermediates in Rat-Liver Mitochondria
Electrical Nature and Coupling of the Exchange-Diffusion Reactions with Proton Translocation
Article first published online: 3 MAR 2005
European Journal of Biochemistry
Volume 22, Issue 1, pages 134–143, September 1971
How to Cite
Papa, S., Lofrumento, N. E., Kanduc, D., Paradies, G. and Quagliariello, E. (1971), The Transport of Citric-Acid-Cycle Intermediates in Rat-Liver Mitochondria. European Journal of Biochemistry, 22: 134–143. doi: 10.1111/j.1432-1033.1971.tb01524.x
- Issue published online: 3 MAR 2005
- Article first published online: 3 MAR 2005
- (Received April B/June 25, 1971)
- 1The electrical nature of the malate-citrate, malate-Pi and malate-2-oxoglutarate exchange diffusion reactions in rat liver mitochondria has been studied. The exchanges have been followed in the presence of respiratory inhibitors and oligomycin to suppress energy supply.
- 2The study of the effect of ionophores and uncouplers on the exchange-diffusion reactions indicates that the citratein-malateout and the malatein-Pi,out exchanges are stimulated by inducing with nigericin or with valinomycin plus carbonyl cyanide p-trifluoromethoxy phenylhydrazone (FCCP) electroneutral influx of H+. These exchanges are unaffected by inducing electrogenic efflux of K+ from mitochondria with valinomycin. The malatein-citrateout exchange appears to be inhibited by electroneutral influx of H+.
- 3Measurement of the extra- and intramitochondrial pH shows that the malate-citrate exchange diffusion is accompanied by translocation of protons, across the mitochondrial membrane, in the same direction as citrate and the Pi-malate exchange by proton translocation in the direction of malate. Evidence is presented that the proton translocation is a direct consequence of the anion exchange.
- 4It is demonstrated that the H+: citrate and the H+: Pi ratios determined experimentally for the malate-citrate and malate-Pi exchanges practically coincide with the theoretical ratios expected for electroneutral malate2-citrate2- and malate2-HPO:2-4 exchanges.
- 5The malate-2-oxoglutarate exchange is not affected by ionophores and/or uncouplers neither it is accompanied by proton translocation across the mitochondrial membrane.
- 6It is concluded that the malate-citrate, malate-Pi and malate-2-oxoglutarate exchange diffusion reactions are electroneutral and that the proton translocation accompanying the malate-citrate and malate-Pi exchanges is determined by the ionization state of malic, citric and phosphoric acid.