Nucleotide/H+‐dependent change in Mg2+ affinity at the ATPase inhibitory site of the mitochondrial F1‐F0 ATP synthase

摘要

>The interactions between ADP and Mg2+ that result in the slowly reversible inhibition of the mitochondrial F₁-F₀ ATPase were studied. The K _i for the inhibitory Mg2+ is shown to be strongly dependent on the occupation of the nucleotide-binding sites. The inhibitory binding site for Mg2+ is not seen unless a stoichiometric amount of ADP is added [Biochem. J. 276 (1991) 149-156]; it appears (K _i = 2.10−6 M) in the presence of stoichiometric ADP and the affinity for inhibitory Mg2+ decreases to a K _i, value of 7.10−5 M when the second nueleotide binding site with k _d = 5.10−6 M is loaded with ADP. The binding of the inhibitory Mg2+ is competitively inhibited by H+ ions within the pH interval 6.8–8.2. The nucleotide-dependent affinity transition of the Mg2+-specific site suggests that H+/Mg2+ exchange may play an important role in the catalytic mechanism of ATP synthesis/hydrolysis at the active site(s) of F₁-F₀ ATP synthase.