Mutation Spectra and the Neutrality of Mutations

Abstract

The effect of amino acid replacements on enzyme function was studied in the tJ-galactosidase of Escherichia coli. Mutants possessing 50% or less of normal enzyme activity were isolated and examined. Of 733 amino acid substitutions calculated to have occurred, only 11 reduced tJ-galactosidase activity below 50 %. These mutations were expressed because they greatly impaired the substrate affinity or catalytic efficiency of the enzyme. The inertness of the enzyme to amino acid replacement was confirmed by immunological tests of tJ-galactosidase molecules changed in amino acid sequence by suppression.