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

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  • JMJohn D. Mcgivan
    John D. Mcgivan
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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. In 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 mainlay in exchange for Pi. The ratio H+/malate is largely independent of the pH despite strong pH dependence of the malate uptake. The citrate/malate exchange is neutralized by the movement of 1 H+ in the direction of both citrate uptake or efflux. 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. The uptake of malate and citrate is increased by respiration. This increase is also dependent on the function of the Pi carrier. For the movement of Pi a ratio H+/Pi= 1.5 at pH 6.9 is obtained, in fair agreement with a theoretical H+/Pi at pH =pK of the dissociation of Pi‐ to Pi2‐. 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. 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.

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