POLYPHOSPHATE KINASE AS A NUCLEOSIDE DIPHOSPHATE KINASE IN ESCHERICHIA-COLI AND PSEUDOMONAS-AERUGINOSA

Generation of a wide variety of nucleoside (and deoxynucleoside) triph osphates (NTPs) from their cognate nucleoside diphosphates (NDPs) is o f critical importance in virtually every aspect of cellular life. Thei r function is fulfilled largely by the ubiquitous and potent nucleosid e diphosphate kinase (NDK), most commonly using ATP as the donor, Cons iderable interest is attached to the consequence to a cell in which th e NDK activity becomes deficient or overabundant. We have discovered a n additional and possibly auxiliary NDK-like activity in the capacity of polyphosphate kinase (PPK) to use inorganic polyphosphate as the do nor in place of ATP, thereby converting GDP and other NDPs to NTPs. Th is reaction was observed with the PPK activity present in crude membra ne fractions from Escherichia coli and Pseudomonas aeruginosa as well as with the purified PPK from E. coli; the activity was absent from th e membrane fractions obtained from E. coli mutants lacking the ppk gen e, The order of substrate specificity for PPK was: ADP > GDP > UDP, CD P; activity with ADP was 2-60 times greater than with GDP, depending o n the reaction condition. Although the transfer of a phosphate from po lyphosphate to GDP by PPK to produce GTP was the predominant reaction, the enzyme also transferred a pyrophosphate group to GDP to form the linear guanosine 5' tetraphosphate.