The Activation of β-Galactosidase by Divalen and Monovalent Cations.

The activation of Escherichia coli K12 3300 β-galactosidase by Na+ and Mg2+ ions appears to involve, apart from effects on the catalytic rate, a complex pattern of interaction between the substrate and the two cations. The time course of activation by Mg2+ can be followed directly by rapid mixing methods; m the presence of Na+ the kinetics of this process is complex, due to the presence of a monomolecular step which becomes rate limiting at high reagent concentrations. The effects produced by Na+, on the other hand, occur rapidly in comparison with the highest attainable rates of catalysis. The activity of defective enzymes from lac- point mutants is also Na+- and Mg2+-dependent. [ABSTRACT FROM AUTHOR]