Electron flow at the polarized mercury-water interface in the presence of membrane fragments rich in Na+−K+-Activated ATPase

Abstract

Measurements of interfacial electron flow indicate that membrane fragments rich in Na(+)-K(+)-ATPase are capable of absorbing and releasing electrons in the form of random currents at an electrode surface. The electron transporting system, which functions in the presence or absence of substrate and activating ions, may be part of or in contact with the enzyme system, but it is not related to the ATPase activity. The observed electron transport at an electrode surface resembles physiological electron transport processes in being reversible, in extending over the same range of potential, and in being affected by some of the chemicals that interfere with electron transport and oxidative phosphorylation in mitochondria. Our experiments do not provide sufficient evidence to identify the substances that are responsible for the random currents, but the results suggest that the electro-active substances are similar to those which are involved in the reactions at the second phosphorylation site in mitochondria. Experiments with this technique provide a new approach to the study of the mechanism of biological electron transport processes and their possible relation to ATP synthesis and hydrolysis.

The properties of rabbit sperm membranes in contact with electrode surfaces

“…Electrode noise due to sperm cell suspensions is similar to that observed in the other particulate systems studied with regard to the dependence of the noise frequency on electrode potential (Blank & Britten, 1970). There is no observable noise at the PZC, which is at about -500 mV, and the noise signals have opposite directions at potentials on the two sides of this point.…”

“…We have attempted to develop new information about the cell membranes of sperm cells by analyzing the noise that the cells generate when in contact with an electrode surface (Blank & Britten, 1970). We have used the mercury/water interface as the electrode, since it is an almost ideal polarizable interface, i.e., an imposed potential will be maintained in the absence of substances that can be oxidized or reduced, with almost no current across the interface.…”

Polarographic studies of membrane particles containing Na−K ATPase

“…1 as well as other experiments involving the membrane fragments all indicate the random currents that have been reported earlier by Blank and Britten (1970). These are apparently due to the presence of particles in the solution since they do not appear in the preparations where the particles are removed by centrifugation and they have been reported in suspensions of surfactants, phospholipids (Blank & Britten, 1970), and inorganic substances (Micka, 1965). The a-c polarograms show that the random currents appear in the region where adsorption occurs in the presence of the "enzyme".…”

“…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…”