Immunochemical characterization of the adenine nucleotide translocator. Organ specificity and conformation...

Antibodies have been prepared against purified preparations of the heart and kidney nucleotide translocator in the 'c'-conformation. The results show organ-specific antigenic determinants on the translocator proteins isolated from heart, kidney and liver although a partial cross-reactivity between these three proteins was demonstrable. The organ specificity was observed both with the solubilized and with the membrane-bound translocator protein indicating organ-specific determinants on exposed regions of the carrier. An organ-specific inhibition of the nucleotide transport in heart mitochondria by the heart carboxyatractylate-protein antiserum leads to the conclusion that the organ specificity is at least partially conditioned by the binding site for the substrate and/or the closely linked gate of the carrier protein. Apart from the organ specificity the results also demonstrate a specificity of the antibodies for the translocational conformations of the carrier: the 'c'-conformation stabilized in the carboxyatractylate-protein complex and the 'm'-conformation present in the bongkrekate-protein complex. However, after denaturation of the carboxytraktylate-protein and bongkrekate-protein complexes the binding of the anti-(carboxyatractylate-protein) antiserum to both inhibitor-protein complexes was nearly identical. The conformation specificity was also expressed by the inhibition of the conformation transition from the 'c'- to the 'm'- state. This side-specific inhibition of the nucleotide transport and the identical binding activity of the carboxyatractylate-protein antiserum against the denatured carboxyatractylate-protein and bongkrekate-protein complexes suggested that the conformation-specific antigenic determinants are topographic surface regions which are determined by the chain folding.