Abstract
The ability to store energy within covalent bonds and to transform this energy into biological reactions is vital for all pro- and eukaryotic cells. Among the wide variety of high-energy compounds, polyphosphate (polyP), a polymer of three to more than a thousand phosphoanhydrid-linked phosphate groups is one of the most ancient energy-rich molecules. Despite its structural simplicity, energy storage is only one of the multiple biological functions of polyP, which we briefly highlight here.