Fig. 1.

The availabilities of metals inside a bacterial cell are set to the inverse of the Irving–Williams series. Metal availabilities have been determined from the sensitivities of DNA-binding, metal-sensing, transcriptional regulators (adapted from reference [6]). The boxes represent the free energies for metal complex formation with proteins that are 80%, 50% or 20% (black to light grey, respectively) metalated in an ideal cell where the metal-sensors are at the mid-points of their dynamic ranges, using the standard equation as shown. Proteins can acquire metal via rapid ligand-exchange reactions with molecules that buffer availabilities to the determined values, only when the free energy gradient is favourable