Abstract
The interrelationships between the effects of Na + and Mg 2+ on β-galactosidase (β- d-galactoside galactohydrolase, EC 3.2.1.23) were studied, together with the inhibition of the enzyme by high concentrations of the two ions and its reactivation on dilution. It was found that the optimum concentration of one ion depended on the concentration of the other and the effect was the opposite of that expected due to ionic strength. The time courses of inhibition and reactivation were found to be different for the two ions. Adjustments of rates on increasing the Mg 2+ concentration to 1.0 M or on diluting from 1.0 M were found to be slow compared to the immediate changes observed with Na +. Substrate was found to partially reverse the Mg 2+ inhibition but had no effect on Na + inhibition or the reactivation with either ion. Increasing the Na + concentration slowed the Mg 2+ inhibition.
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