Dibutyltin‐3‐hydroxyflavone titrates a dissociable component (cofactor) of mitochondrial ATP synthase: An energy‐transfer component linked to the ubiquinone pool

Abstract

Dibutyltin‐3‐hydroxyflavone, Bu2Sn(of), is a new fluorescence probe inhibitor of F1F0‐ATPase and oxidative phosphorylation which inhibits by titration of an unidentified component of F0. Its site of action is closely related to that of the trialkyltins and of venturicidin. This F0 component is part of a pool of this component which is present in the heart mitochondrial inner membrane at levels of 5–7 nmol (mg protein)−1 [18 ± 3 Bu2Sn(of) sites per mol F1F0‐ATPase]. However, ATPase activity in submitochondrial particles is near maximally inhibited by titration of approx. three Bu2Sn(of) sites per mol F1F0‐ATPase. Over 60% (60–80%) of the Bu2Sn(of) interaction sites can be lost during the purification of F1F0‐ATPase from submitochondrial particles. The number of Bu2Sn(of) interaction sites in various F1F0‐ATPase preparations is variable. The high numbers of Bu2Sn(of) sites per mol F1F0‐ATPase for heart mitochondria (18–21) and submitochondrial particles (15–19.5) decline in ATP synthase (11–15) to the low values obtained in Complex V (7–10.5) and the minimal values observed in highly purified F1F0−ATPase (3.5–5.6), thus indicating a variable dissociable component or cofactor of ATP synthase. The Bu2Sn(of) interaction site, a component of ATP synthase, is responsive to the redox status of the respiratory chain and the interaction with Bu2Sn(of) is with the reduced form of this component. Fluorescence titration studies show that this component is in redox equilibrium with the ubiquinone pool of the respiratory chain. It is proposed that this redox component serves as an inhibitor titratable cofactor pool which cycles through an F0 interaction site (or sites) via a system which serves as an energy‐transfer link between the respiratory chain and ATP synthase.

The vacuolar H+-ATPase: a universal proton pump of eukaryotes

“…Both F-and V-ATPases show sensitivity to alkyl tin compounds [135,[180][181][182][183][184]. These lipophilic compounds appear to interact with V o at or close to the site of DCCD action [135], and presumably therefore inhibit proton translocation specifically, further indicating the proximity of the proton-translocating pathway to the lipid phase.…”