COLD LABILITY OF THE MUTANT FORMS OF ESCHERICHIA-COLI INORGANIC PYROPHOSPHATASE

The variants of Escherichia coli pyrophosphatase carrying the substitu tions Glu20-->Asp, His136-->Gln or His140-->Gln are inactivated, in co ntrast to the wild-type enzyme, at temperatures below 25 degrees C: th eir activity measured at 25 degrees C decreases with decreasing the te mperature of the stock enzyme solution. The inactivation is completely reversible and is explained by cold-induced dissociation of these hex americ enzymes into less active trimers.