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 pyrophosphatas e (PPase) activities of the same organelle. Heparin, an effective inhi bitor of the nuclear polyphosphatase activity, does not alter the ATPa se and PPase activities. The nuclear polyphosphatase activity is optim al 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 organelle s of the same yeast. The polyphosphatase activity is nearly the same w ith 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 hydr olysis of polyphosphates with chain lengths (n) over bar = 3, 15, and 208 are 100, 5, and 4.1 mu M, respectively. The nuclear polyphosphatas e activity differs in some properties from that of cell envelope, cyto sol, and vacuoles of the same S. cerevisiae strain.