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Figure S1. Curves obtained when plotting the rates of ATP cleavage against ouabain concentrations were analyzed using the following equations to determine pseudomaximal activity of α1 and α3-α3 isozymes (V_α1 and V_α2/3, respectively): V = V_α1 + V_α2-3 and V_i = [(V_max - V_min)/(1 + ([X] /I₅₀)ⁿ) + V_min ], where V is the hydrolytic activity, V_max/min are maximal and minimal rates of Pi production, [X] is a concentration of ouabain, and I₅₀ is a concentration of ouabain causing a 50% inhibtion of the Na/K ATPase. Fitting was based on the assumption the Hill coefficient n = 1, α V_min = 0, and performed using Origin 7.0 software (Microcal Software, Inc.). Data used for curve plotting were mean values of seven independent experiments and standard deviations obtained for each point were included into the analyses as weight coefficient W_i = 1/SD²_i. Thus, standard errors of the I₅₀ and V_max computed as chi-square during the iterating procedure included the SD for each point.