Inhibition of Na⁺, K⁺-ATPase by Hydrostatic Pressure

Abstract

We investigated the influence of hydrostatic pressure on the activity of the Na⁺, K⁺-ATPase from rabbit kidney. The activity of the enzyme was determined using a kinetic assay which couples ATP hydrolysis to NADH oxidation. The decrease of NADH fluorescence intensity was measured in a high-pressure optical cell. In this paper we present first experimental results. The data show that the activity of Na⁺, K⁺-ATPase is inhibited reversibly by pressures below 2 kbar. At higher pressures, the enzyme is inactivated irreversibly, however. The plot of ln(activity) vs. pressure is essentially linear, thus allowing for the calculating of an apparent activation volume of the pressure-induced inhibition reaction which amounts to ΔV ^≠ = 47.1 ± 2.3 mL mol⁻¹. The inhibition might be induced by a pressure-induced ordering of the acyl-chains of the lipid matrix or due to subunit dissociation.