CHARACTERISTICS OF THE CYTOSOL POLYPHOSPHATASE ACTIVITY OF THE YEAST SACCHAROMYCES-CEREVISIAE

The organelle-free cytosol fraction of Saccharomyces cervisiae cells e xhibit polyphosphatase activity corresponding to about 65% of that of protoplast homogenate. The polyphosphatase activity is optimal at pH 6 .5-7.5. Bivalent metal cations stimulate the cytosol polyphosphate act ivity in the series Zn2+ > Co2+ > Mg2+, Mn2+, increasing the activity 9 to 14-fold. Fe2+, Cu2+, and Ca2+ inhibit the activity at all tested concentrations. Ammonium molybdate and heparin effectively inhibit the polyphosphatase activity. The inhibition by heparin is competitive an d occurs only in the presence of Mg2+, Mn2+, or Co2+, but not with Zn2 +. The polyphosphatase activity is nearly the same with substrates ran ging from poly(P)(9) to poly(P)(208). The values of K-mapp for hydroly sis of poly(P)(9), poly(P)(15), and poly(P)(208) are 19, 11, and 1.2 m u M, respectively. Gel filtration on Sephacryl S-300 gives a molecular weight of about 50 kD for the cytosol pyrophosphatase.