The inositol monophosphatase from bovine brain is inactivated by the histidine-specific reagent diethylpyrocarbonate. Using 4 mM reagent at pH 6.5, the reaction results in the modification of 3 equivalents of histidine per polypeptide chain. The loss of activity occurs at the same rate as the slowest reacting of these residues. Site directed mutagenesis studies have been used to generate a mutated enzyme species bearing a His-217→Gln replacement and have shown that it is the modification of histidine 217 which results in the inactivation of the enzyme.
