A kinetic model for the action of the inorganic pyrophosphatase from bakers' yeast. The activating influence of magnesium ions.

A systematic analysis of the kinetics of the crystallized inorganic pyrophosphatase from bakers' yeast is presented. The complications arising from the existence of various complexes between magnesium and pyrophosphate are obviated to a large extent by choosing the free metal Mg2+ and the 1:1 complex of magnesium and pyrophosphate as the concentration variables. Out of a great number of possible kinetic models the one best fitting the experimental data was selected by computer model fitting. It is an equilibrium model in which magnesium acts as an activator and the 1:1 complex of magnesium and pyrophosphate is the substrate. It has been shown that from the two possible species of the 1:1 complex at pH 7.2 either the unprotonated form is the true substrate or the unprotonated and protonated forms together are alternative substrates. Spectroscopic binding studies support the conclusions drawn from the kinetics.

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