Tributyltin (TBT) effect on the mitochondrial F0F1 complex in the Mytilus galloprovincialis digestive gland.

The biochemical mechanisms involved in mollusc TBT toxicity remain at least in part unknown and TBT effects on mollusc mitochondria have up to now been poorly elucidated. The mitochondrial oligomycin sensitive Mg-ATPase (OS-MgATPase), amounting to 80% of total mitochondrial MgATPase, was progressively depressed by increasing TBT concentrations up to a maximal inhibition of 70% at 0.7 μM TBT. Lineweaver Burk and Dixon plots exhibited the typical shape of an apparently non-competitive inhibition with respect to the ATP substrate with a Ki value of 0.23 μMTBT. MgATPase inhibition was partially released within the 0.7–5.0 μM TBT range up to a 70% activity recovery at 5.0 μM TBT. At higher TBT concentrations, OS-MgATPase activity appeared to be once again progressively depressed attaining nearly 100% enzyme inhibition at 30 μM TBT. A parallel increase in an oligomycin insensitive MgATPase (OI-MgATPase) activity was progressively observed. The hypothesis of a TBT-driven removal of F1 subunit from the ATPase complex was excluded by incubation and centrifugation procedures followed by convenient ATPase activity assays. Quercetin, a selective F1 inhibitor, prevented the OI-MgATPase activity increase at higher than 5.0 μM TBT, thus suggesting that F1 is not involved in TBT inhibitory mechanism and shouldering the hypothesis that F0 subunit is the target of TBT.