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The transport of inorganic phosphate by the mitochondrial dicarboxylate carrier
Abstract:
1. N-Ethylmaleimide inhibited the influx and efflux of P(i) in rat liver mitochondria. 2. The efflux was stimulated by either succinate or malate in the presence of N-ethylmaleimide, and this stimulation was reversed by 2-n-butylmalonate. 2-Oxoglutarate and citrate, even in the presence of low concentrations of malate, were relatively ineffective in stimulating efflux of P(i) under these conditions, as was glutamate. 3. By using radioactively labelled P(i) and dicarboxylate ions an exchange was demonstrated, the stoicheiometry of which was 1.3+/-0.5 dicarboxylate ions:1 P(i) (n=10). 4. An exchange between unlabelled and labelled P(i) in the presence of N-ethylmaleimide was found which was sensitive to 2-n-butylmalonate. 5. It is concluded that the mitochondrial dicarboxylate carrier can transport phosphate by an exchange diffusion with certain penetrant dicarboxylic acids or with phosphate itself. The exchange mechanism is sensitive to 2-n-butylmalonate but is unaffected by N-ethylmaleimide; the action of mersalyl in this context is commented on.
Insights
Rat liver mitochondria utilize the dicarboxylate carrier to transport phosphate (P(i)). This transport occurs via exchange diffusion with dicarboxylic acids or phosphate, and is modulated by 2-n-butylmalonate.
Area of Science:
- Mitochondrial physiology
- Membrane transport
- Biochemistry
Background:
- Mitochondria play a crucial role in cellular energy metabolism.
- Phosphate transport across the inner mitochondrial membrane is essential for ATP synthesis.
- The dicarboxylate carrier is known to transport dicarboxylic acids.
Purpose of the Study:
- To investigate the role of the mitochondrial dicarboxylate carrier in phosphate transport.
- To elucidate the mechanism and regulation of phosphate (P(i)) transport in rat liver mitochondria.
Main Methods:
- Utilized N-ethylmaleimide to inhibit mitochondrial transport.
- Employed radioactively labeled phosphate (P(i)) and dicarboxylate ions to study exchange mechanisms.
- Assessed the effects of succinate, malate, 2-oxoglutarate, citrate, glutamate, and 2-n-butylmalonate on P(i) transport.
Main Results:
- N-Ethylmaleimide inhibited both influx and efflux of P(i).
- Succinate or malate stimulated P(i) efflux in the presence of N-ethylmaleimide, an effect reversed by 2-n-butylmalonate.
- Demonstrated a stoichiometric exchange between P(i) and dicarboxylate ions (1.3:1 ratio).
- Identified a 2-n-butylmalonate-sensitive P(i) exchange mechanism unaffected by N-ethylmaleimide.
Conclusions:
- The mitochondrial dicarboxylate carrier facilitates phosphate transport via exchange diffusion.
- Phosphate can be exchanged for penetrant dicarboxylic acids or other phosphate molecules.
- The transport mechanism is sensitive to 2-n-butylmalonate but not N-ethylmaleimide.