Mai Okada

Hiroshima University, Hirosima, Hiroshima, Japan

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Publications (2)5.79 Total impact

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    ABSTRACT: Inorganic polyphosphate (polyP) is a linear polymer of tens to hundreds of phosphate (Pi) residues linked by "high-energy" phosphoanhydride bonds as in ATP. PolyP kinases, responsible for the synthesis and utilization of polyP, are divided into two families (PPK1 and PPK2) due to differences in amino acid sequence and kinetic properties. PPK2 catalyzes preferentially polyP-driven nucleotide phosphorylation (utilization of polyP), which is important for the survival of microbial cells under conditions of stress or pathogenesis. Phylogenetic analysis suggested that PPK2 family could be divided into three subfamilies (class I, II, III). Class I and II PPK2 catalyze nucleoside diphosphate and nucleoside monophosphate phosphorylation, respectively. Here we demonstrated that class III PPK2 catalyzes both nucleoside monophosphate and nucleoside diphosphate phosphorylation, thereby enabling us to synthesize ATP from AMP by a single enzyme. Moreover, class III PPK2 showed broad substrate specificity over purine and pyrimidine bases. This is the first demonstration that class III PPK2 possesses both class I and II activities.
    Applied and Environmental Microbiology 02/2014; 80(8). DOI:10.1128/AEM.03971-13 · 3.67 Impact Factor
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    ABSTRACT: Intracellular phosphate (P(i) ) is normally maintained at a fairly constant concentration in Escherichia coli, mainly by P(i) transport systems and by the 'phosphate balance' between P(i) and polyphosphate (polyP). We have reported previously that excess uptake of P(i) in a phoU mutant results in elevated levels of polyP. Here, we found that the elevated levels of polyP in the mutant could be reduced by the overproduction of YjbB, whose N-terminal half contains Na(+) /P(i) cotransporter domains. The rate of P(i) export increased when the YjbB overproducer grew on a medium containing glycerol-3-phosphate. These results strongly suggested that YjbB reduced the elevated levels of polyP in the phoU mutant by exporting intracellular excess P(i) .
    FEMS Microbiology Letters 07/2011; 320(1):25-32. DOI:10.1111/j.1574-6968.2011.02285.x · 2.12 Impact Factor