A hybrid mutant form of Escherichia coli inorganic pyrophosphatase.

The inorganic pyrophosphatase of Escherichia coli is a tightly hexamer of identical subunits. Upon interaction of its two mutant forms in which the trimer-trimer contacts were weakened because of E20D and H136Q substitutions, a hybrid hexameric E20D/H136Q-PPase is formed. The catalytic activity of its constituent H136Q trimer is same of its hexamer, whereas metal-binding affinity is significantly decreased. These results point to an interdependence of two trimers in catalysis by hexameric pyrophosphatase.