Characterization of the polyphosphatase activity of Saccharomyces cerevisiae nuclei

Saccharomyces cerevisiae nuclei possess polyphosphatase activity which is insensitive to a number of inhibitors of ATPase and pyrophosphatase (PPase) activities of the same organelle. Heparin, an effective inhibitor of the nuclear polyphosphatase activity, does not alter the ATPase and PPase activities. The nuclear polyphosphatase activity is optimal at pH 7.5 and is stimulated by bivalent metal cations in the series: Co2+ > Mg2+> Zn2+ > Mn2+. The stimulation is, however, considerably less than that for the polyphosphatase activities from other organelles of the same yeast. The polyphosphatase activity is nearly the same with polyphosphates ranging from (n) over bar = 9 to (n) over bar = 208, but it is 1.5-fold higher with tripolyphosphate. K-m values for hydrolysis of polyphosphates with chain lengths (n) over bar = 3, 15, and 208 are 100, 5, and 4.1 mu M, respectively. The nuclear polyphosphatase activity differs in some properties from that of cell envelope, cytosol, and vacuoles of the same S. cerevisiae strain.