Abstract
The F1F0 complex of Paracoccus denitrificans (PdF1F0) is the fastest ATP synthase but the slowest ATPase. Sulfite exerts maximal activation of the PdF1F0-ATPase (Pacheco-Moisés, F., García, J. J., Rodríguez-Zavala, J. S., and Moreno-Sánchez, R. (2000). Eur J. Biochem. 267, 993-1000) but its effect on the PdF1F0-ATP synthase activity remains unknown. Therefore, we studied the effect of sulfite on ATP synthesis and 32Pi <--> ATP exchange reactions of inside-out membrane vesicles of P. denitrificans. Sulfite inhibited both reactions under conditions of maximal delta pH and normal sensitivity to dicyclohexylcarbodiimide. Sulfite increased by 10- and 5-fold the K0.5 for Mg2+-ADP and Pi during ATP synthesis, respectively, and by 4-fold the IC50 of Mg2+-ADP for inhibition of the PdF1F0-ATPase activity. Thus, sulfite exerts opposite effects on the forward and reverse functioning of the PdF1F0 complex. These effects are not due to membrane or PdF1F0 uncoupling. Kinetic and structural modifications that could account for these results are discussed.
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