Purification and characterization of highly active and stable polyphosphatase from Saccharomyces cerevisiae cell envelope

Saccharomyces cerevisiae cell envelope polyphosphatase was isolated in highly active and stable form by extraction from cells with zwittergent TM-314 followed by chromatography of the extract on phosphocellulose and QAE-Sephadex in the presence of 5 mM -MgCl₂, 0·5 mM -EDTA and 0·1% Triton X-100. The enzyme possessed a specific activity of 220 U/mg and after 30 days retained 87% of its activity at ?20°C. Polyphosphatase molecular mass was determined to be about 40 kDa by gel filtration and polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The enzyme hydrolysed polyphosphates with various chain lengths (n = 3–208), had low activity for GTP and did not split pyrophosphate, ATP and p-nitrophenylphosphate. On polyphosphates with chain lengths n = 3, 9 and 208, K_m values were 1·7 × 10^?4, 1·5 × 10^?5 and 8·8 × 10^?7 M respectively. Polyphosphatase was most active and stable at pH 6·0–8·0. The enzyme showed maximal activity at 50°C. The time of half inactivation of polyphosphatase at 40, 45 and 50°C was 45, 10 and 3 min, respectively. In the absence of divalent cations and also with Ca²⁺ or Cu²⁺, the enzyme showed practically no activity. The ability of divalent cations to activate polyphosphatase was reduced in the following order: Co²⁺ > Mg²⁺ > Mn²⁺ > Fe²⁺ > Zn²⁺. Polyphosphatase was completely inhibited by 1 mM -ammonium molybdate and 50 μM -Zn²⁺ or Cu²⁺ (in the presence of Mg²⁺).