THE N-TERMINUS AND C-TERMINUS OF THE TRICARBOXYLATE CARRIER ARE EXPOSED TO THE CYTOPLASMIC SIDE OF THE INNER MITOCHONDRIAL-MEMBRANE

Polyclonal antibodies were raised in rabbits against two synthetic pep tides corresponding to the N- and C-terminal regions of the rat-liver mitochondrial tricarboxylate carrier, ELISA tests performed with intac t and permeabilized rat-liver mitoplasts showed that both anti-N-termi nal and anti-C-terminal antibodies bind only to the cytoplasmic surfac e of the inner membrane, indicating that both termini of the membrane- bound tricarboxylate carrier are exposed to the mitochondrial intermem brane space, Furthermore, tryptic digestion of intact mitoplasts marke dly decreased the binding of anti-N-terminal and anti-C-terminal antib odies to the tricarboxylate carrier, These results are consistent with an arrangement of the tricarboxylate carrier monomer into an even num ber of transmembrane segments, with the N- and C-termini protruding to ward the cytosol.