THE BETA- d -GALACTOSIDASE OF ESCHERICHIA COLI, STRAIN K-12

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Abstract
Beta-D-Galactosidase was extracted from adapted cells of E. coli. strain K-12. A method of assay was based upon the colorimetric detn. of nitrophenol released from a new chromogenic substrate, o-nitrophenyl-beta-D-galac-toside. The kinetics of hydrolysis of this substrate indicated a close fit to the Michaelis theory. Alkali metal ions influenced the efficiency and affinities of the enzyme. Other galactoside substrates, i.e., lactose, methyl, n-butyl, and sorbityl analogs, lactobionic acid, and galactose itself combined with the enzyme and could be considered competitive inhibitors. The dissociation constants for each of these compounds was determined. The galactosidase activity of intact cells was activated by drying and autolytic procedures. This accounted for the previously drawn conclusion that adaptation and genetic competence are based upon permeability differences.