Sulfite Stimulates the ATP Hydrolysis Activity of but not Proton Translocation by the ATP Synthase of Rhodobacter Capsulatus and Interferes with its Activation by Δ_H+

Abstract

Sulfite stimulates the rate of ATP hydrolysis by the ATP synthase in chromatophores of Rhodobucter capsulatus. The stimulated activity is inhibited by oligomycin. The activation takes place also in uncoupled chromatophores. The activation consists in an increase of about 12-15-fold of the V,,,,, for the ATP hydrolysis reaction, while the K,,, for MgATP is unaffected at 0.16i0.03 mM. The dependence of V,,,,, on the sulfite concentration follows a hyperbolic pattern with half maximum effect at 12 mM.Sulfite affects the ability of the enzyme in translocating protons. Concomitant measurements of the rate of ATP hydrolysis and of ATP-induced protonic tlows demonstrate that at sulfite concentrations of greater than 10 mM the hydrolytic reaction becomes progressively uncoupled from the process of proton translocation. This is accompanied by an inhibition of ATP synthesis, either driven by light or by artificially induced ionic gradients. ATP synthesis is totally inhibited at concentrations of at least 80 mM.Sulfite interferes with the mechanism of activation by d P H , . Low concentrations of this anion ( S 2 mM) prevent the activation by A$,,+. At higher concentrations a marked stimulation of the activity prevails, regardless of the occurrence of a AFHt across the membrane. Phosphate at millimolar concentrations can reverse the inhibition by sulfite.These experimental results can be simulated by a model assuming multiple and competitive equilibria for phosphate or sulfite binding with two binding sites for the two ligands (for sulfite K,, = 0.26 and K2? = 37 mM, and for phosphate K , , = 0.06 and K2p = 4.22 mM), and in which the state bound only to one sulfite molecule is totally inactive in hydrolysis. The competition between phosphate and sulfite is igands and of the enzyme.ATP-driven proton translocation; protonic slipping; consistent with the molecular structures of the two

Sulfite and membrane energization induce two different active states of the Paracoccus denitrificans F0F1‐ATPase

“…Therefore, activation of the PdF 0 F 1 ‐ATPase by sulfite is partially due to increased membrane energization. Similar results have been found in R. capsulatus chromatophores and is described as autoactivation of the ATPase in the presence of sulfite [14,33].…”

“…However, in contrast to the increase of ATPase activity, higher concentrations of sulfite failed to exert a further increase in the ATP‐driven fluorescence quenching. In recent similar results with Rhodobacter capsulatus chromatophores, it was proposed that sulfite induced a partially uncoupled active state of the enzyme which was, however, oligomycin‐sensitive [33]. In P. denitrificans membranes, the sulfite‐activated ATPase was venturicidin and oligomycin‐sensitive (Table 1).…”

Energy-dependent Transformation of F0·F1-ATPase in Paracoccus denitrificans Plasma Membranes

“…3), in coupled P. denitrificans vesicles, great precautions should be taken if the enzyme activity is to be quantitatively characterized, and the optimal level of ⌬ H ϩ dissipation should be determined for any particular preparation under given conditions. At present, we do not know whether sulfite-protected active ATPase in P. denitrificans vesicles is fully coupled or uncoupled, as has been demonstrated for Rhodobacter capsulatus membranes (37). We were unable to follow ⌬ response in the presence of sulfite because of non-enzymatic interaction of the latter with Oxonol VI.…”

“…B, the residual rates of ATP hydrolysis (20 s after the deactivation was started as described in A) were measured as a function of ADP concentration. (37)(38)(39)(40)…”

Purification and Biochemical Characterization of the F1-ATPase fromAcidithiobacillus ferrooxidansNASF-1 and Analysis of theatpOperon

“…1) In Rhodobacter capsulatus, the sulfite-activated state is unable to translocate protons across the membrane or to promote chemiosmotic ATP synthesis, and the mechanism of sulfite activation probably involves two binding sites, with which phosphate binding can interfere. 28) In Paracoccus denitrificans, sulfite functioned as a nonessential activator that slightly modified the affinity for ATP and increased the V max . 29) Since sulfite is an intermediate of sulfur oxidation in A. ferrooxidans, activation of ATPase activity by sulfite ion appeared to be possible in A. ferrooxidans cell.…”