PPX1 was the first gene related to inorganic polyphosphate (poly P) metabolism isolated from a eukaryotic cell (1). Poly P is a chain of tens or many hundreds of phosphate (Pi) residues linked by high-energy phosphoanhydride bonds. PPX1 encodes a potent cytoplasmic exopolyphosphatase, responsible for hydrolyzing poly P into Pi residues (2). The enzyme acts as an exoenzyme in a processive mode releasing Pi residues from the ends of poly P chain (2). The enzyme is a monomer with a molecular mass of 40 kDa (2). For optimal activity the enzyme depends on divalent metal ions, which may bind the enzyme in addition to chelating the poly P chain (2). The yeast Ppx1p is much more active than its E. coli counterpart and acts on substrate poly P chains of a broader size range (i.e., 3 to 1000 residues). It does not act on pyrophosphate, ATP, or the cyclic form of tripolyphosphate (2). Mutants lacking Ppx1p have normal growth phenotype (2); several other polyphosphatases are known in yeast which might replace its function (4, 5).

Last updated: 2001-11-15