An exopolyphosphatase (polyPase) with a specific activity of 60 U/mg protein has been purified from the vacuolar sap of Saccharomyces cerevisiae. The molecular mass of the intact enzyme was found to be 245 kDa. It is highly specific towards high-molecular polyphosphates (polyP). The activity with polyP9 is 24% of that with polyP208. The apparent Km for polyP15 and polyP208 hydrolysis is 93 and 2.4 microM, respectively. The enzyme is slightly active with polyP3 and adenosine-5'-tetraphosphate, but does not hydrolyze pyrophosphate, ATP, GTP and p-nitrophenylphosphate. It is stimulated by divalent metal cations. Co2+, the best activator, stimulates it 6-fold. Antibodies that inhibit the cell envelope and cytosol polyPases of S. cerevisiae have no effect on the vacuolar polyPase. The vacuolar polyPase differs from other yeast polyPases in molecular mass, substrate specificity and effects of activators.
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Andreeva et al. (1998) studied this question.
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