A STUDY OF THE MITOCHONDRIAL F1-ATPASE TRYPTOPHAN PHOSPHORESCENCE AT 273-K

The bovine heart mitochondrial F-1-ATPase complex exhibits an intrinsi c tryptophan phosphorescence that can be used to monitor structural ch anges of the E-subunit. The phosphorescence decay rate of F, containin g the tightly bound nucleotides increases upon addition of adenine nuc leoside triphosphate in the presence of magnesium. The average phospho rescence lifetime of this enzyme preparation decreases from 10.2 to 7. 8 ms upon Mg-ATP addition. Since increasing phosphorescence decay rate is related to increasing flexibility of proteins, Mg-ATP added to the F-1-ATPase complex can enhance the flexibility of the protein structu re surrounding the chromophore. Experiments carried out on F-1 prepare d with the three noncatalytic sites filled and the three catalytic sit es vacant show a significant increase of the phosphorescence lifetime from 6.4 ms to 7.6 ms upon Mg-ATP addition. These results suggest that the mitochondrial F-1-ATPase epsilon-subunit conformation senses diff erently the nucleoside triphosphate binding to catalytic or noncatalyt ic sites. (C) 1995 Academic Press. Inc.