Since 28Mg2+ is practically unobtainable, much of the old data will need to be reinterpreted with new tools for measuring Mg2+ transport, if different transporters are to be compared directly. The pioneering work of Kolisek and Froschauer using mag-fura 2 has shown that free Mg2+ can be reliably measured in vivo in some systems. By returning to the analysis of CorA with this new tool, we have gained an important baseline for the analysis of new Mg2+ transport systems as they are discovered. However, it is important that the amount of transporter present in the membrane is accurately determined if comparisons of transport capability are to be made. This bacterial system might also be able to provide some utility for the analysis of eukaryotic Mg2+ transport proteins, but differences in biological systems of prokaryotes and eukaryotes will have to be considered in any experiment. Function Comparing the functions of the characterised Mg2+ transport proteins is currently almost impossible, even though the proteins have been investigated in different biological systems using different methodologies and technologies. Finding a system where all the proteins can be compared directly would be a major advance. If the proteins could be shown to be functional in bacteria (S. typhimurium), then a combination of the techniques of mag-fura 2, quantification of protein in the envelope membrane, and structure of the proteins (X-ray crystal or cryo-TEM) might allow the determination of the basic mechanisms involved in the recognition and transport of the Mg2+ ion. However, perhaps the best advance would be the development of methods allowing the measurement of the protein's function in the patch-clamp system using artificial membranes. Bacteria Early research In 1968, Lusk described the limitation of bacterial (Escherichia coli) growth on Mg2+-poor media, suggesting that bacteria required Mg2+ and were likely to actively take this ion from the environment. The following year, the same group and another group, Silver, independently described the uptake and efflux of Mg2+ in metabolically active E. coli cells using 28Mg2+. By the end of 1971, two papers had been published describing the interference of Co2+, Ni2+ and Mn2+ on the transport of Mg2+ in E. coli and in Aerobacter aerogenes and Bacillus megaterium. In the last major development before the cloning of the genes encoding the transporters, it was discovered that there was a second Mg2+ uptake system that showed similar affinity and transport kinetics to the first system, but