Mechanism of action of bicarbonate and sulfate on the mitochondrial ATPase

ANABELLA LODEYRO; OSCAR A. ROVERI

Villa Carlos Paz, ARGENTINA.

Congreso; XXXVIII Reunión Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2002

Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

MECHANISM OF ACTION OF BICARBONATE AND SULFATE ON THE MITOCHONDRIAL ATPase. The mitochondrial ATPase catalyses ATP synthesis and hydrolysis coupled to H+ translocation. Bicarbonate stimulates ATP hydrolysis and inhibits ATP synthesis. The inhibition is competitive towards ADP and non-competitive with Pi (1). Sulfate behaves as a partial inhibitor of ATP hydrolysis and as a linear competitive inhibitor towards Pi of ATP synthesis (2). ATP hydrolysis was inhibited by sulfate at [ATP] < 2 mM and stimulated at higher [ATP]. Since maximal inhibition decreased with increasing [ATP] and similar IC0.5 or A0.5 values were estimated at different [ATP], it can be concluded that sulfate behaves as a non essential activator that increases kcat and decreases the apparent affinity for ATP. The results obtained when the effect of mixtures of both anions on ATP synthesis and hydrolysis was studied showed that they bind to different sites on the ATPase. This result is consistent with our previous suggestion (1) that bicarbonate binds to a non-catalytic nucleotide site in place of ADP/ATP and with the report (3) that sulfate binds to a catalytic site in place of Pi. However, since sulfate behaves as a partial inhibitor of ATP hydrolysis, we must conclude that ATP can productively bind to the enzyme even in its presence. 1)       Lodeyro et al. (2001) Biochim. Biophys. Acta 1506, 236–243 2)       Lodeyro and Roveri (2002)  XIV International Biophysics Congress 3)       Menz et al (2001) Cell 106, 331 – 341.