The Activity of Individual Molecules of Hybrid β‐Galactosidase Reconstituted from the Wild‐Type and an Inactive‐Mutant Enzyme

A technique capable of detecting individual molecules of β‐galactosidase has been used to measure the enzyme activity of single hybrid β‐galactosidase molecules reconstituted from mixtures of varying proportions of wild‐type and lac−aba mutant enzyme. Reconstituted molecules exhibit activities of 0, 1/4, 2/4, 3/4, 4/4 of the wild‐type enzyme, depending on the ratio of wild‐type to mutant subunits. These results are expected if each of the four active sites of the Escherichia coliβ‐galactosidase is independently active.