Accumulation of Sulfate by Mitochondria of Rat Kidney Cortex

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Abstract
Twice washed mitochondria from rat kidney cortex can accumulate sulfate ions from low (10-7M) ambient concentrations to create virtual gradients of several hundred to one. This sulfate is subsequently released. The activation energy for the uptake is 12,000 calories per mole; for release it is about 30,000 calories per mole. Variations in the sulfate concentration of the medium show that there is a straight line Freundlich adsorption isotherm over a million-fold range of concentration of sulfate in the medium. There are 9 x 104 sites at 10-5 Mand 9x 105 sites at 10-3 Msulfate per average single mitochondrion. Preincubation at 30[degree]C rapidly destroys ability to accumulate sulfate. Partial protection occurs if oxidative phosphory-lation is proceeding during the preincubation. The concentration of the endogenous inorganic sulfate of twice washed mitochondria is 4.2 x 10-4 moles per liter of mitochondrial pellet water; 99.85 per cent of this endogenous sulfate is inexchangeable with external sulfate in vitro. It is all exchangeable in vivo. The pH optimum for accumulation of radio-sulfate from dilute external sulfate concentrations is 5.5. These observations show that there is a delicate and specific mechanism in mitochondria from kidney cortex which accumulates sulfate. The chemical nature of the accumulated sulfate is unknown.