Kinetic characterization of a thermostable inorganic pyrophosphatase from Thermus thermophilus.

A kinetic characterization was performed for inorganic pyrophosphatase from Thermus thermophilus. The optimum activity with Mg2+ as the activating metal ion lies in a pH range between 8.3 and 9.5. The hydrolysis of inorganic pyrophosphate is also activated by Zn2+, Mn2+, and Co2+. Calcium ions are not activating at all. Tripolyphosphate is another substrate hydrolyzed by the enzyme but only with Zn2+ as the activating metal ion. Other potential substrates like ATP and cyclic metaphosphates are not hydrolyzed even at high enzyme concentrations. Computer modelling of kinetic data obtained from activity measurements with different total magnesium ion and pyrophosphate concentrations confirms a kinetic model which was shown to be valid also for inorganic pyrophosphatases from other microbial sources. The corresponding parameter values are given. The inorganic pyrophosphatase from T. thermophilus exhibits extremely high thermostability which is decreased by addition of EDTA indicating a stabilizing effect of divalent metal ions.