Multiple molecular forms of β-galactosidase

In uninduced lactose-fermenting strains of Escherichia coli, β-galaetosidase migrated as a single rapidly moving eleotrophoretic component which, on sucrose gradient centrifugation, has a sedimentation coefficient of 16 s. On induction, at least 7 eleotrophoretic forms of the enzyme appeared, the slowest of which had a sedimentation coefficient of 34 s. Values for the Michaelis constant of the 16 and 34 s forms were similar. Evidence is presented that this pattern is stable and reproducible in vitro, and reversible in vivo. Nearly identical patterns of galactosidase activity were seen in constitutive bacteria and in various hybrid strains containing an episome derived from E. coli. It is concluded that these forms represent higher molecular weight aggregates of β-galactosidase. A significant portion of the thiogalactoside transacetylase also existed as high molecular weight forms as detected by electrophoresis and density-gradient centrifugation, and could be disaggregated by dialysis or the presence of iso-propyl-β-D-thiogalactoside.