Dissociation and catalytic activity of oligomer forms of β-galactosidases

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The dissociation of oligomer forms of bacterial Escherichia coli, yeast Kluyveromices fragilis, and bovine liver β-galactosidases was studied. The catalytic constants for the dimers and tetramers of the bacterial enzyme, dimers and monomers of the animal enzyme, and dimers of the yeast enzyme in the reaction of hydrolysis of 2-nitrophenyl-β-D-galactopyranoside were determined. At 25°C, these values were found to be 180 and 400 s−1 for the bacterial enzyme, 0.01 and 0.08 s−1 for the bovine liver enzyme, and 45.4 s−1 for the yeast enzyme, respectively. The other oligomer forms of the β-galactosidases were inactive under conditions of these experiments.