35S-Atractyloside binding affinity to the inner mitochondrial membrane

Isolated inner mitochondrial membrane contains a small number of binding sites for atractyloside (of the order of 0.1 nmole/mg of protein) with very high binding affinity (half saturation at 0.014 &mgr;M atractyloside). The high affinity binding ability of the inner mitochondrial membrane is markedly decreased upon aging, acidification of the medium or addition of ADP, but remains unchanged in the presence of uncouplers such as FCCP. Added ADP causes a two-step transition from the high affinity binding to low affinity binding (K(d) > 0.50 &mgr;M) and concomitantly a significant increase of the measured number of binding sites (about a doubling). The half maximum effect in the first step transition is given by 1 &mgr;M ADP. The use of 35S-atractyloside as a probe of the inner mitochondrial membrane conformation specifically related to the adenine nucleotide translocation is discussed.