J. B. Chappell

THE ANION TRANSPORTING SYSTEMS OF MITOCHONDRIA AND THEIR BIOCHEMICAL SIGNIFICANCE

Abstract There appear to be three ways in which anions may enter or leave mitochondria. These are (i) by anion-hydroxyl exchange (or anion-proton symport) [e.g. the phosphate transporter]; (ii) by anion-anion exchange [e.g. the malate-phosphate antiporter, the citrate-malate antiporter]; (iii) electrophoretically. This type of entry mechanism may be sub-divided into two classes. The first, uniport of a single anion [e.g. nitrate, thiocyanate, or iodide in the presence of a trace of iodine (I3−)] or antiport of an uncharged species for a negatively or positively charged species [e.g. glutamate and perhaps ornithine for citrulline]. The biochemical significance of these transporting systems, especially that of amino acid systems, is discussed.