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Articles

Citrate Transport in Corn Mitochondria ¹

Department of Botany, University of Illinois, Urbana, Illinois 61801

Citrate uptake by corn mitochondria (Zea mays L. B73 x Mol9) was investigated by osmotic swelling and [¹⁴C]citrate accumulation. Uptake driven by passive influx, ammonium gradients, and respiration was followed. There was no requirement for phosphate and/or malate to secure citrate uptake, although under some conditions these additives were promotive. Inhibition of the phosphate and dicarboxylate carriers did not eliminate citrate uptake. Citrate_in/malate_out exchange occurs, but at a rate too slow to account for observed citrate uptake, and depletion of endogenous malate only reduced citrate uptake by 38%. It was concluded that citrate can be rapidly accumulated by a mechanism other than by exchange for dicarboxylates. The effect of uncoupler on respiration-driven [¹⁴C]citrate accumulation, and studies of passive swelling using ionophores and uncouplers indicated that the major avenue of citrate uptake is by H⁺/citrate co-transport with a pH optimum near 4.5. The in vivo role of this mechanism is not yet understood.

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				G. Genchi, A. Spagnoletta, A. De Santis, L. Stefanizzi, and F. Palmieri Purification and Characterization of the Reconstitutively Active Citrate Carrier from Maize Mitochondria Plant Physiology, July 1, 1999; 120(3): 841 - 848. [Abstract] [Full Text]