THE TF1-ATPASE AND ATPASE ACTIVITIES OF ASSEMBLED ALPHA(3)BETA(3)GAMMA, ALPHA(3)BETA(3)GAMMA-DELTA, AND ALPHA(3)BETA(3)GAMMA-EPSILON COMPLEXES ARE STIMULATED BY LOW AND INHIBITED BY HIGH-CONCENTRATIONS OF RHODAMINE 6G WHEREAS THE DYE ONLY INHIBITS THE ALPHA(3)BETA(3), AND ALPHA(3)BETA(3)DELTA COMPLEXES

The ATPase activity of the F-1-ATPase from the thermophilic bacterium PS3 is stimulated at concentrations of rhodamine 6G up to about 10 mu M where 70% stimulation is observed at 36 degrees C. Half maximal stim ulation is observed at about 3 mu M dye. At rhodamine 6G concentration s greater than 10 mu M, ATPase activity declines with 50% inhibition o bserved at about 75 mu M dye. The ATPase activities of the alpha(3) be ta(3) gamma and alpha(3) beta(3) gamma delta complexes assembled from isolated subunits of TF1 expressed in E. coli deleted of the une opero n respond to increasing concentrations of rhodamine 6G nearly identica lly to the response of TF1. In contrast, the ATPase activities of the alpha(3) beta(3) and alpha(3) beta(3) delta complexes are only inhibit ed by rhodamine 6G with 50% inhibition observed, respectively, at 35 a nd 75 mu M dye at 36 degrees C. The ATPase activity of TF1 is stimulat ed up to 4-fold by the neutral detergent, LDAO. In the presence of sti mulating concentrations of LDAO, the ATPase activity of TF1 is no long er stimulated by rhodamine 6G, but rather, it is inhibited with 50% in hibition observed at about 30 mu M dye at 30 degrees C. One interpreta tion of these results is that binding of rhodamine 6G to a high-affini ty site on TF1 stimulates ATPase activity and unmasks a low-affinity, inhibitory site for the dye which is also exposed by LDAO.