Confining the Sodium Pump in a Phosphoenzyme Form: The Effect of Lead(II) Ions

Abstract

The effect of Pb(2+) ions on the Na(+),K(+)-ATPase was investigated in detail by means of steady-state fluorescence spectroscopy. Experiments were performed by using the electrochromic styryl dye RH421. It is shown that Pb(2+) ions can bind reversibly to the protein and do not affect the Na(+) and K(+) binding affinities in the E(1) and P-E(2) conformations of the enzyme. The pH titrations indicate that lead(II) favors binding of one H(+) to the P-E(2) conformation in the absence of K(+). A model scheme is proposed that accounts for the experimental results obtained for backdoor phosphorylation of the enzyme in the presence of Pb(2+) ions. Taken together, our results clearly indicate that Pb(2+) bound to the enzyme stabilizes an E(2)-type conformation. In particular, under conditions that promote enzyme phosphorylation, Pb(2+) ions are able to confine the Na(+),K(+)-ATPase into a phosphorylated E(2) state.

A Method to Measure Hydrolytic Activity of Adenosinetriphosphatases (ATPases)

“…The enzymatic method of Schwartz et al [33] is a rapid and easy test that can be performed on ATPases, as reported in the literature [34], [35]. On the other hand, PK and LDH enzymes usually need a careful storage (e.g.…”

Lead poisoning: acute exposure of the heart to lead ions promotes changes in cardiac function and Cav1.2 ion channels

“…Differential effects of Pb 2+ have been reported regarding Na + /K + pump activity in different cells (Fox et al 1991). Although the binding affinities for Na + and K + are not affected, exposure to Pb 2+ seems to restrict the pump to a phosphorylated state (the E2 conformational state) (Bartolommei et al 2010).…”