Tributyltin (TBT) inhibition of oligomycin-sensitive Mg-ATPase activity in mussel mitochondria

Tributyltin (TBT), one of the most toxic lipophilic aquatic pollutants, can be efficiently incorporated from sea water and sediments by filter-feeding molluscs. As far as we are aware TBT effects on the mitochondrial oligomycin-sensitive Mg-ATPase, the enzymatic core of energy production and a known target of TBT toxicity in mammals, have not been yet investigated in molluscs; thus the hydrolytic capability of the mitochondrial complex in the presence of micromolar concentrations of TBT was assayed in the mussel Mytilus galloprovincialis. Gill and mantle ATPase activities were progressively depressed by increasing TBT doses up to a maximal inhibition (82% in the gills and 74% in the mantle) at 0.62 μM TBT. Non-cooperative inhibition kinetics (nH ∼ −1) and a non-competitive mechanism with respect to ATP substrate were pointed out. The mitochondrial Mg-ATPase susceptivity to TBT in the marine mussel was consistent with the formation of a TBT–Mg-ATPase complex, apparently more stable in the gills than in the mantle. The complex shape of the dose-response curve and the partial release of Mg-ATPase inhibition within the 0.6–34.4 μM TBT range suggest multiple interactions of TBT with the enzyme complex putatively related to its molecular mechanism of toxicity.