Tightly bound adenosine diphosphate, which inhibits the activity of mitochondrial F1‐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 F₁-ATPase results in a decrease in the initial rate of ATP hydrolysis. The addition of an equimolar amount of ATP to the nucleotide depleted F₁-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 F₁-ATPase catalytic site (uni-site catalysis). The F₁-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_½ 20 s) or (ii) binding of P_i in addition to MgADP and the formation of the triple F₁-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 F₁-ATPase. It is proposed that ATP-dependent dissociation of the F₁-ATPase-GDP complex occurs more rapidly, than that of the F₁-ATPase-ADP complex.