Membrane‐linked energy transductions. Bioenergetic functions of sodium: H+ is not unique as a coupling ion

Abstract

The concept is developed according to which Na+, like H+, can play the role of a coupling ion in energy‐transducing biomembranes. This idea is based on observations that (i) Na+ can be extruded from the cell by primary pumps (Na‐motive NADH‐quinone reductase, decarboxylase or ATPase), and (ii) the downhill Na+ flux into the cell can be coupled with the performance of all the three types of membrane‐linked work i.e. chemical (ATP synthesis), osmotic (accumulation of solutes) and mechanical (motility). Marine alkalotolerant Vibrio alginolyticus represents the first example of such a complete sodium cycle pattern. Simplified versions of the sodium cycle or some of its constituents are found in the cytoplasmic membrane of a great variety of taxa including anaerobic, aerobic and photosynthetic bacteria, cyanobacteria and animals; this fact indicates that Na+ energetics should be regarded as a common case, rather than a rare exception applyed to some natural niches only. Copyright © 1985, Wiley Blackwell. All rights reserved