[Comparative kinetic studies of Mg2+-activated hydrolysis of tripolyphosphate and pyrophosphate by inorganic pyrophosphatase].

Computer analysis of P3 and pyrophosphate conversion rate dependence on substrate and metal-activator concentrations reveals the identity of kinetic patterns. Dissociation and catalytical constants for the enzyme combinations with two types of metal-substrates complexes, MS and M2S, at pH 9.0 are by one to two orders of magnitude "poorer" for P3 as compared to PPi. Optimal pH value for the hydrolysis of P3 is by 2 units higher than this for the hydrolysis of PPi. pH profiles for the kinetic parameters in the pH range 8.0--9.5 differ considerably for the two substrates, presumably due to the existence of additional catalitically important ionisations in the reaction with P3.