Hydrolysis of tripolyphosphate by purified exopolyphosphatase from Saccharomyces cerevisiae cytosol: Kinetic model

The kinetics of hydrolysis of tripolyphosphate by purified exopolyphosphata se from Saccharomyces cerevisiae cytosol has been studied in the presence o f Mg2+. Two kinetic models suggesting the formation of complexes of tripoly phosphate and the enzyme with Mg2+ are compared. Both models suggest that o nly enzyme substrate complexes containing Mg2+ and tripolyphosphate simulta neously are able to hydrolyze the tripolyphosphate. The first model suggest s that the enzyme is able to bind to Mg2+ independently from substrate bind ing. The second model does not consider this possibility, but suggests that both complexes containing tripolyphosphate and Mg2+ in proportion 1:1 and 1:2 can serve as the reaction substrates. The description of the experiment al data by both models is essentially the same. The complex containing trip olyphosphate and Mg2+ in proportion 1:1 is optimal for the enzyme activity, the complex containing tripolyphosphate and Mg2+ in proportion 1:2 being h ydrolyzed at a lower tate.