6'-O-dansyl-gamma-aminobutyryl atractyloside, a fluorescent probe of the ADP/ATP carrier: exploration of conformational changes of the membrane-bound ADP/ATP carrier elicited by substrates and inhibitors.

A fluorescent atractyloside analogue, the 6'-O-dansyl-gamma-aminobutyryl atractyloside (DGA), has been used to probe the binding of the inhibitors carboxyatractyloside (CATR) and bongkrekic acid (BA) and nucleotide substrates to the membrane-bound ADP/ATP carrier protein in beef heart mitochondria. Binding and release of DGA were followed by fluorescence responses. Specifically bound DGA was fully released by CATR alone, or by BA in the presence of micromolar amounts of ADP. In the absence of the inhibitors, ADP increased the rate of the specific binding of DGA. The effect of ADP was shared by transportable nucleotides. Non transportable nucleotides were ineffective. These data are consistent with the previously described CATR and BA conformations of the ADP/ATP carrier that are able to bind CATR and BA respectively, the transition between the two conformations being accelerated by micromolar concentrations of transportable nucleotides.