The protein VAT-1 from Torpedo electric organ exhibits an ATPase activity

VAT-1 is an abundant protein in Torpedo electric organ which copurifies with a major ATPase activity from synaptic vesicles. VAT-1 was expressed in E. coli and the product was purified and analyzed. The protein binds specifically to an ATP column and displays an ATPase activity as measured by the kinetics of [32P]phosphate release. The activity is dependent on divalent ions, with both Mg2+ and Ca2+ supporting the reaction. The apparent Km for ATP is 18 microM. This ATPase activity is not affected by known inhibitors of the vesicular V- and P-type ATPases such as vanadate and N-ethylmaleimide. We suggest that VAT-1 activity may affect ATP-dependent reactions in Torpedo nerve terminals, such as phosphorylation and dephosphorylation of proteins.