Nucleotide/H +-dependent change in Mg 2+ affinity at the ATPase inhibitory site of the mitochondrial F 1-F 0 ATP synthase

Abstract

The interactions between ADP and Mg 2+ that result in the slowly reversible inhibition of the mitochondrial F 1-F 0 ATPase were studied. The K i for the inhibitory Mg 2+ is shown to be strongly dependent on the occupation of the nucleotide-binding sites. The inhibitory binding site for Mg 2+ 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 Mg 2+ 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 Mg 2+ is competitively inhibited by H + ions within the pH interval 6.8–8.2. The nucleotide-dependent affinity transition of the Mg 2+-specific site suggests that H +/Mg 2+ exchange may play an important role in the catalytic mechanism of ATP synthesis/hydrolysis at the active site(s) of F 1-F 0 ATP synthase.