Measurements on the Distribution of <i>E. coli</i> β-Galactosidase Electrophoretic Mobilities Suggest Heterogeneous Ligand Binding

The distribution of electrophoretic mobility of E. coli β-galactosidase was measured in the presence of citrate, α-ketoglutarate, oxaloacetate, and pyrophosphate and compared to that of the enzyme in the absence of ligand. In the presence of citrate the mobility was found to significantly shift toward a more negative value and the range in mobilities was found to significantly increase. This was attributed to heterogeneous binding of citrate. Electrophoretic theory suggests that this increase in range can be attributed to the difference of up to three citrates bound to any given enzyme molecule.