Tributyltin sensitivity of vacuolar-type Na+-transporting ATPase from Enterococcus hirae

Abstract

Tributyltin chloride (TBT), an environmental pollutant, is toxic to a variety of eukaryotic and prokaryotic organisms. Some members of F-ATP synthase (F-ATPase)/vacuolar type ATPase (V-ATPase) superfamily have been identified as the molecular target of this compound. TBT inhibited the activities of H +-transporting or Na+-transporting F-ATPase as well as H+-transporting V-ATPase originated from various organisms. However, the sensitivity to TBT of Na+-transporting V-ATPase has not been investigated. We examined the effect of TBT on Na+-transporting V-ATPase from an eubacterium Enterococus hirae. The ATP hydrolytic activity of E. hirae V-ATPase in purified form as well as in membrane-bound form was little inhibited by less than 10 μM TBT; IC50 for TBT inhibition of purified enzyme was estimated to be about 35 μM. Active sodium transport by E. hirae cells, indicating the in vivo activity of this V-ATPase, was not inhibited by 20 μM TBT. By contrast, IC50 of H+-transporting V-ATPase of the vacuolar membrane vesicles from Saccharomyces cerevisiae was about 0.2 μM. E. hirae V-ATPase is thus extremely less sensitive to TBT.