The most abundant cation found in the cytoplasm of living things is the potassium ion. Inside the cell the concentration of potassium ions is above 100 mM, while outside the cell the potassium ion concentration is usually less than 5 mM. Potassium ion channels are essential elements in cellular electrical excitability while also main-taining a resting potential in non-excitable cells. Potassium ion channels selectively conduct potassium ions over sodium ions by a factor of 1000:1. Genes that encode potassium channels are found in nearly all genomes, including those of bacteria and archaea. Thallium ions are among several ion species that are known to permeate potassium ions channels; they have a radius of 1.40 A˚ , which is very similar to the 1.33 A˚ radius of a potassium ion. Here you can see an example where the potassium ions were replaced by Thallium (yellow spheres) in the channelling pocket of a K+ selective transporter isolated from Bacillus cereus. The structure was determined by X-ray diffraction (PDB code: 8CTV)

#molecularart ... #immolecular ..: #channel ... #potassium ... #thallium ... #replacement ... #xray ... #bacillus

Structure rendered with @proteinimaging and depicted with @corelphotopaint