Dibutyltin (DBT) is a powerful inhibitor of the digestive gland mitochondrial Mg-ATPase in Mytilus galloprovincialis.

Organotin compounds are lipophilic pollutants especially dangerous to aquatic biota. Trisubstituted species and especially n-tributyltin (TBT), widely exploited in the past in antifouling paints, are long known as the most harmful toxicants to membrane systems. Mitochondria are a preferred target of organotins, currently defined as mitochondrial poisons. DBT is generally considered as a far less effective toxicant. In digestive gland mitochondria from Mytilus galloprovincialis the OS-Mg-ATPase activity was in vitro inhibited by μmolar concentrations of both TBT and DBT individually tested and even more strongly by the latter. The main difference between the two organotin effects was shown by the inhibition curve shape. While the TBT inhibition curve displayed a complex hormetic profile tentatively ascribed to multiple TBT-enzyme interactions, the enzyme inhibition curve by DBT was hyperbolic as enzyme inhibition gradually increased with increasing DBT concentrations. At higher than 5 µM TBT concentrations, an apparent loss of the enzyme susceptivity to its specific inhibitor oligomycin, resulting into a striking rise in the OI Mg-ATPase was observed; conversely DBT did not affect the OI Mg-ATPase. The different behaviour of the two organotins could be related to their different interaction capability with crucial ATPase domains. The elucidation of the kinetic mechanisms involved in the Mg-ATPase inhibition by organotins deserves further studies.