Fig. 9. Structural unfolding and enzymatic inhibition by urea of foot muscle Na⁺/K⁺-ATPase from active and estivating snails. Enzyme extracts were denatured overnight with different concentrations of urea and then either treated with thermolysin or assayed under optimal conditions. (A) Mean relative Na⁺/K⁺-ATPase protein remaining (as quantified from band intensities on western blots) after overnight incubation with urea and subsequent proteolysis with thermolysin; values are means ± s.e.m., N=3 independent trials. (B) Mean relative activity of foot muscle Na⁺/K⁺-ATPase from active and estivating snails as a function of overnight incubation with different concentrations of urea; values are means ± s.e.m., N=3.