61] Cation transport in cyanobacteria

Abstract

This chapter considers the systems responsible for cation transport in cyanobacteria, excluding proton and NH 4 +3 transport. Cells use both primary and secondary transport systems for ion translocation across their membranes. Primary systems couple chemical energy directly to the performance of electrochemical work resulting in an ion gradient. In the reversed mode osmotic energy can be coupled to chemical bond formation. In bacteria as well as in eukaryotic cells, demonstration of the existence of a particular ion-transport system, and determination of its apparent kinetics and energy source, can be achieved in intact cells. Measurement of intracellular ion concentration, as dependent on extracellular concentration and on cellular metabolic state, is the routine experiment for identifying an active transport system in vivo. For calculation of intracellular ion concentration it is assumed that the intracellular ion is free in solution. The intracellular osmotic volume can be determined by any of the techniques already published and thoroughly discussed. An innovative approach for measuring intracellular volume has been recently developed in cyanobacteria. This method is based on spin-labeled, metabolically inert, small molecules that rapidly equilibrate across the cytoplasmic membrane.