Significance Polyphosphate kinases (PPKs) are involved in many metabolic processes in bacteria, including pathogenic species. As these enzymes are not present in animals, they are a prime target for the development of novel antibiotics. The detailed knowledge of the mechanism of action and structure–function relationships of these enzymes is of utmost importance for the identification and design of new pharmaceutically active compounds and the rational improvement of lead structures. In addition, PPKs use inexpensive and stable polyphosphate as a phosphate donor and phosphorylate nucleoside 5′-mono- as well as 5′-diphosphates. This makes them of special interest for application in ATP regeneration systems, which can be efficiently coupled to ATP-consuming enzymes in environmentally friendly and sustainable biotechnological processes.