Tightly bound adenosine diphosphate, which inhibits the activity of mitochondrial F 1-ATPase, is located at the catalytic site of the enzyme

Abstract

The binding of one ADP molecule at the catalytic site of the nucleotide depleted F 1-ATPase results in a decrease in the initial rate of ATP hydrolysis. The addition of an equimolar amount of ATP to the nucleotide depleted F 1-ATPase leads to the same effect, but, in this case, inhibition is time dependent. The half-time of this process is about 30 s, and the inhibition is correlated with P i dissociation from the F 1-ATPase catalytic site (uni-site catalysis). The F 1-ATPase-ADP complex formed under uni-site catalysis conditions can be reactivated in two ways: (i) slow ATP-dependent ADP release from the catalytic site (τ 1 2 20 s) or (ii) binding of P i in addition to MgADP and the formation of the triple F 1-ATPase-MgADP-P i complex. GTP and GDP are also capable of binding to the catalytic site, however, without changes in the kinetic properties of the F 1-ATPase. It is proposed that ATP-dependent dissociation of the F 1-ATPase-GDP complex occurs more rapidly, than that of the F 1-ATPase-ADP complex.