Catalytic activity profile of polyP:AMP phosphotransferase from Myxococcus xanthus.

Myxococcus xanthus generates polyphosphates (polyPs) during starvation and forms fruiting bodies through the activity of polyphosphate kinase (Ppk). M. xanthus polyP:AMP phosphotransferase (Pap), a class II Ppk2, catalyzes the transfer of the terminal phosphate from polyP to AMP to yield ADP, but its enzymatic properties have not been investigated in detail. In this study, we found that Pap was activated by Mn or Mg and required higher concentrations of these ions in reactions with longer polyPs to demonstrate maximum activity. The K of Pap for polyP was significantly lower than that for shorter polyPs, but the highest catalytic constant (k) was observed for polyP. When Pap was incubated with polyP and AMP for 3 h, it first generated ADP and then gradually produced ATP, suggesting that M. xanthus Pap also has polyP:ADP phosphotransferase activity similar to that of class III Ppk2 enzymes. During starvation, the specific activity of Pap in M. xanthus was increased by 2.3-2.4-fold at days 1 and 2 of incubation. In addition, recombinant Pap in combination with M. xanthus recombinant enzymes Ppk1 or adenylate kinase (AdkA) could generate ATP from AMP and polyP. These results suggest a functional role of Pap during M. xanthus starvation, when it might act in cooperation with Ppk1 and/or AdkA to produce ATP from AMP, ADP, and polyP.