The N- and C-termini of the tricarboxylate carrier are exposed to the cytoplasmic side of the inner mitochondrial membrane.

Polyclonal antibodies were raised in rabbits against two synthetic peptides corresponding to the N- and C-terminal regions of the rat-liver mitochondrial tricarboxylate carrier. ELISA tests performed with intact and permeabilized rat-liver mitoplasts showed that both anti-N-terminal and anti-C-terminal antibodies bind only to the cytoplasmic surface of the inner membrane, indicating that both termini of the membrane-bound tricarboxylate carrier are exposed to the mitochondrial intermembrane space. Furthermore, tryptic digestion of intact mitoplasts markedly decreased the binding of anti-N-terminal and anti-C-terminal antibodies to the tricarboxylate carrier. These results are consistent with an arrangement of the tricarboxylate carrier monomer into an even number of transmembrane segments, with the N- and C-termini protruding toward the cytosol.