| Abstract: | Fluorescent 3'-O-acyl-substituted adenine nucleotide (dimethylamino)naphthoyl and trinitrophenyl groups were studied for binding to the ADP/ATP carrier in mitochondria and submitochondrial particles. The changes in fluorescence intensity and emission maximum are for the most part similar to those observed in nonaqueous solvents. The (dimethylamino)naphthoyl derivatives from a largely quenched aqueous state have a shortwave shift up to 85 nm and increase up to 90-fold (1,5 derivative), whereas the little quenched naphthoyl derivatives show a fluorescence decrease and the weakly fluorescent trinitrophenyl derivative shows only a small increase on binding. All derivatives are good inhibitors (K1 = 1-10 microM) of nucleotide transport. The fluorescence titrations have an apparent K1/2 = 2-7 microM. The fluorescence of the 1,5-DAN nucleotide is fully suppressed by bongkrekate but only partially suppressed by carboxyatractylate. The fluorescence response is much stronger in submitochondrial particles than in mitochondria. Both facts suggest fluorescent binding to the "m" state of the carrier site at the inner face of the membrane. 1,5-DAN-AMP shows a slightly more efficient binding than DAN-ADP or DAN-ATP. |
