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Effects of metal-fluoride complexes on the phosphatase activity of the PMCA Saffioti N.A, Ferreira Gomes, M.S., de Sautu M., Rossi, J.P. and Mangialavori I.C. IQUIFIB- Facultad de Farmacia y Bioquímica, UBA. irenem@qb.ffyb.uba.ar Plasma membrane calcium pump (PMCA) belongs to the P-type family of active cation pumps. According to the conventional E1?E2 theory, E1 and E2 are the high and low-affinity states for Ca2+, respectively. When the pump in the E1 state hydrolyses ATP, it generates an auto-phosphorylated intermediate E1-P which transform to E2-P. This conformational change allows the calcium release. Besides of this phosphorylase activity, it have been described a phosphatase activity where the E2 conformation hydrolyze p-nitrophenylphosphate in the absence of Ca2+ (1). Vanadate and metal fluorides like magnesium, beryllium, and aluminum (MexFy), act as phosphate analogues and inhibit P-type ATPases, by interacting with the phosphorylation site. In the sarcoplasmic calcium pump, these metal-fluoride complexes stabilize analogues of E2P in different conformations (2). In order to study the effects on PMCA, we characterized the phosphatase activity and conformational changes of a purified preparation of PMCA, in the presence of these fluoride-complexes. Our results show that MexFy inhibit phosphatase activity hyperbolically, with a similar behavior, except with magnesium fluoride which exhibits a more complex manner. The apparent inhibition constants were different from those obtained for the phosphorylase activity in the same conditions. We also detected conformational changes with the fluorescent probe TNP-ATP when these complexes bind to PMCA, showing different structural changes of E2 intermediates. With grants from UBACYT, ANPCYT y CONICET 1- Mazzitelli I R, Adamo H P. Biochimica et Biophysica Acta. 2007. 1777. 2- Clausen J D. The Journal of Biological Chemistry. 2011. 11792