Active Ionic Transport across Biological Membranes: Possible Role of Electrons and Protons

Abstract

THE conversion of metabolic energy into useful work is a very efficient process in biological cells. The energy in ATP is transformed into mechanical, electrical and osmotic work at efficiencies which have been calculated to approach 100 per cent for acid secretion in the stomach¹, active Na⁺ transport in frog skin² and sartorius muscle contraction³. These observations show that energy is converted in biological cells by a process which is not limited by a Carnot efficiency factor (about 2 per cent in warm blooded animals). The process could involve electrochemical “cold” combustion, in which chemical energy is transformed into electronic potential energy, in much the same way as the operation of a fuel cell⁴. Accordingly, Mitchell^5,6 likened the oxido/reduction and phosphorylation processes in his chemiosmotic hypothesis to a protonic fuel cell in which ATP synthesis was construed as a vectorial reaction driven by a “proton-motive” force across the mitochondrial membrane.