Inhibition of steady-state mitochondrial ATP synthesis by bicarbonate, an activating anion of ATP hydrolysis

ANABELLA F. LODEYRO; NORA B. CALCATERRA; OSCAR A. ROVERI

BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS

Elsevier

Lugar: Amsterdam (Holanda); Año: 2001 vol. 1506 p. 236 - 243

0005-2728

Bicarbonate, an activating anion of ATP hydrolysis, inhibited ATP synthesis coupled to succinate oxidation in beef heart submitochondrial particles but diminished the lag time and increased the steady-state velocity of the 32Pi-ATP exchange reaction. The latter effects exclude the possibility that bicarbonate is inducing an intrinsic uncoupling between ATP hydrolysis and proton translocation at the level of F1Fo ATPase. The inhibition of ATP synthesis was competitive with respect to ADP at low fixed [Pi], mixed at high [Pi] and non-competitive towards Pi at any fixed [ADP]. From these results we can conclude that (i) bicarbonate does not bind to a Pi site in the mitochondrial F1; (ii) it competes with the binding of ADP to a low-affinity site, likely the low-affinity non-catalytic nucleotide binding site. It is postulated that bicarbonate stimulates ATP hydrolysis and inhibits ATP synthesis by modulating the relative affinities of the catalytic site for ATP and ADP.