Correlation Between H⁺ and Anion Movement in Mitochondria and the Key Role of the Phosphate Carrier

Abstract

The mechanism according to which anions such as di-and tricarboxylates are accumulated in mitochondria are investigated with respect to H+ movement and the role of the Pi carrier.1. I n the absence of respiration, malate is taken up mainly by net accumulation with H+/malate = 1.6. When corrected for exchange with Pi, H+/malate = 2 is found. Under aerobic conditions malate is taken up mainly in exchange for Pi. The ratio H+/malate is largely independent of the pH despite strong pH dependence of the malate uptake.2. The citratelmalate exchange is neutralized by the movement of 1 H+ in the direction of both citrate uptake or efflux.3. The net uptake of malate and citrate is abolished by SH reagents demonstrating a key role of the Pi carrier in the net accumulation of di-and tricarboxylates.4. The uptake of malate and citrate is increased by respiration. This increase is also dependent on the function of the Pi carrier.5. For the movement of Pi a ratio H+/Pi = 1.5 a t pH 6.9 is obtained, in fair agreement with a theoretical H+/Pi a t pH = p K of the dissociation of Pi-to Pi2-.6. Anion distribution not coupled to the Pi carrier, such as the distribution of glutamate, is not linked to H+ movement and to energy-linked accumulation. 7. The role of the H+ gradient and of energy coupling via the Pi carrier in maintaining different redox potentials across the inner mitochondrial membrane is discussed.It is generally accepted that the penetration of substrate anions through the mitochondrial membrane is mediated by specific transport systems. Evidence for the existence of these carriers has been reviewed recently 11-31. The various anion exchanges catalyzed have been clarified by the use of specific inhibitors 14-81, but problems of functional relationship between these anion carriers have not yet been elucidated.The uptake of anions by mitochondria is dependent on pH and it has been shown that the distribution of anions in inhibited mitochondria is quantitatively related to the pH gradient across the membrane [9]. There i s some preliminary evidence that the uptake of Pi is directly coupled to H+ movement while that of malate is not [lo, 111 (cf. also 1121). The uptake of malate and citrate by respiring mitochondria is higher than that by respiration-inhibited mitochondria, and this effect does not depend on cation movement [13].I n this paper, the relationship between substrate anion and Hf movement in tho absence of cation movements is investigated. It is shown here that the pH-dependent uptake of dicarboxylates, oxoglutarate Unusual Abbreviations. Ethylene glycol bis @-aminoethyl)-N,N-tetraacetic acid, EGTA; p-trifluoromethoxycarbonylcyanidephenylhydrazone, FCCP.--and citrate is mediated through the Pi carrier, which has been discussed earlier, as a catalyst for the net uptake of these substrates [13a]. The increased uptake of these anions in the respiring mitochondria is mediated by an effect of energy on Pi transport.The relation of these findings to the redox equilibrium of NAD in the cytoplasm and mitochondria is di...

Proton movement accompanying monocarboxylate permeation in hemoglobin‐free perfused rat liver

“…Another possibility would be that only a constant fraction of the intracellular space would reveal net H+ changes whereas other compartments respond differently. Recently, a correlation between H' and Pi and malate movement in isolated rat liver mitochondria gave a stoichiometry factor of unity [9]. Preliminary results on the stoichiometry for benzoate and H+ movement in the perfused liver indicate that it may be below unity.…”

Analysis of the Reactivity of SH-Reagents with the Mitochondrial Phosphate Carrier

“…17). The Pi binding site of the carrier is assumed to exist in a neutral (C) and cationic (CH+) (protonized) form with a pK = 7 so that at [7,11,12,10]. It has been suggested [12] that the H+ dissociation takes place a t the Pi so that only the acid form of Pi (e.g.…”

Effects of hormones and N6O2′-dibutyryl-adenosine 3′ :5′-cyclic monophosphate, administered in vivo, on phosphate transport and metabolism in isolated rat liver mitochondria

“…Titheradge & Coore, 1976;Halestrap, 1977; 1978 Yamazaki et al, 1977). The magnitude of this gradient appears to be the major driving force for the net transport of phosphate by mitochondria (McGivan & Klingenberg, 1971;Lehninger, 1974;Coty & Pedersen, 1975 (Pestka, 1971), although the possibility that in the presence of both glucagon and cycloheximide the concentration of cyclic AMP is decreased (cf. Wititsuwannakul & Kim, 1977) cannot be excluded.…”

“…Changes in mitochondrial phosphate transport may be involved in regulating the supply of Pi to the mitochondrial matrix for the reactions of oxidative phosphorylation. Furthermore, the transport of phosphate is closely linked to that of ADP and Ca2+ and is an obligatory requirement for the net transport of malate, a-oxoglutarate and citrate (McGivan & Klingenberg, 1971;Lehninger, 1974;Coty & Pedersen, 1975;Reed & Bygrave, 1975).…”