* To whom correspondence should be addressed.
Received January 12, 2009; Revision received February 11, 2009
Endopolyphosphatase activity has been revealed in cytosol preparations of the yeast Saccharomyces cerevisiae with inactivated PPX1 and PPN1 genes encoding exopolyphosphatases. The enzyme cleaves inorganic polyphosphates with chain length of 15 to 208 phosphate residues to shorter chains without the release of orthophosphate (Pi). The long chain polyphosphates are cleaved with preference over the short ones. Heparin, a known inhibitor of exopolyphosphatases, represses this activity. The endopolyphosphatase activity is not stimulated by Mg2+ or Co2+, in contrast to exopolyphosphatases. This activity along with a pyrophosphatase is supposed to be responsible for polyphosphate utilization as a phosphate reserve in a mutant devoid of exopolyphosphatases.
KEY WORDS: inorganic polyphosphates, endopolyphosphatase, exopolyphosphatase, cytosol, PPX1 and PPN1 mutant, Saccharomyces cerevisiae