Polarographic studies of membrane particles containing Na−K ATPase

Abstract

Summary. The properties of a suspension of membrane particles containing Na-K ATPase have been investigated with the aid of d --c and a --c polarography. In particular, we have studied the interaction of three cations, two very effective enzyme inhibitors and one activator, with the enzyme preparation. Ag + and Cu ++, which inhibit the enzyme at very low concentrations, bind very strongly. No binding could be found with the activating ion, T1 +, however. Adsorption of a substance with an isoelectric point between pH 4 and pH 5.5 occurred at the electrode surface between -0.1 and -1.2 V at pH 7, and was associated with the random currents that appear during the measurements. The random currents arise when the membrane particles collide with the electrode and cause changes in the structure of the electrical double layer. (Added substances that adsorb more strongly at the mercury/water interface eliminate the random currents.) The adsorbed film impedes the flow of the free Ag + and Cu ++ ions, and to a smaller extent, the flow of T1 + ions. The differences between the binding of inhibiting and activating ions are correlated with their effects on the ATPase enzyme activity.The Na-K-acfivated ATPase, which is found in the membrane fractions of many tissues, is believed to be involved in the active transport of Na § and K § ions across cell membranes (Skou, 1965). The energy for the transport and enzymic processes comes from the hydrolysis of ATP, which proceeds by the phosphorylation of a membrane component (requiring the presence of Na + and Mg++), followed by hydrolysis of the intermediate (requiring the presence of K+). The way in which the Na § and K § ions activate the enzyme system, and are themselves transported as a result of the reaction, is unknown and has been the subject of many studies.In a recent paper (Blank & Britten, 1970), we described some properties of membrane particles containing Na-K ATPase in contact with a mercury electrode surface. In the presence of these particles, one could detect random

The properties of rabbit sperm membranes in contact with electrode surfaces

“…The random currents in cell suspensions are due to changes in the electrical double layer at the mercury/water interface when a particle hits the electrode surface and causes changes in adsorption (Bach, Britten & Blank, 1973). On contact, the cell surface competes with the electrode surface for adsorbed material and this can lead to a transfer of adsorbate.…”