Degradation of polyphosphates by polyphosphate kinases from Ruegeria pomeroyi

Polyphosphate kinases 2 (PPK2) are key enzymes for polyphosphate utilisation in bacteria. The genome of Ruegeria pomeroyi, a marine α-proteobacterium, includes three Pseudomonas aeruginosa PPK2 homologs. We expressed these homologs in Escherichia coli as soluble proteins, purified the protein products and compared their metal, pH and nucleotide preferences. The optimal pH was 8.0 for SPO1727 and 9.0 for SPO1256. The SPO0224 gene product had two pH optima at eight and ten. The SPO0224 protein showed little dependence on metal presence, while SPO1256 required Mg(2+). SPO1727 required Mg(2+) but accepted other ions as well.