Complete inhibition and partial re-activation of single F1-ATPase molecules by tentoxin -: New properties of the re-activated enzyme

During hydrolysis of ATP, the gamma subunit of the rotary motor protein F-1-ATPase rotates within a ring of alpha(3)beta(3) subunits. Tentoxin is a phyto-pathogenic cyclic tetrapeptide, which influences F-1-ATPase activity of sensitive species. At low concentrations, tentoxin inhibits ATP hydrolysis of ensembles of F-1 molecules in solution. At higher concentrations, however, ATP hydrolysis recovers. Here we have examined how tentoxin acts on individual molecules of engineered F-1-ATPase from the thermophilic Bacillus PS3 (Groth, G., Hisabori, T., Lill, H., and Bald, D. ( 2002) J. Biol. Chem. 277, 20117 - 20119). We found that inhibition by tentoxin caused a virtually complete stop of rotation, which was partially relieved at higher tentoxin concentrations. Re-activation, however, was not simply a reversal of inhibition; while the torque appears unaffected as compared with the situation without tentoxin, F-1 under re-activating conditions was less susceptible to inhibitory ADP binding but displayed a large number of short pauses, indicating infringed energy conversion.