EFFECT OF ALCOHOLS ON ENZYMATIC ACTIVITY AND SUBUNIT ASSOCIATION OF BETA-GALACTOSIDASE

The catalytic activity of β-galactosidase from Escherichia coli K12 and the associative properties of its subunits have been studied in solutions of methanol, ethanol, i-propyl- and n-propyl alcohol. All of the alcohols at low concentrations (5%) stimulate the rate at which o-nitrophenyl-β-d-galactopyranoside is cleaved. The transferase activity of the enzyme was demonstrated by identification of methyl β-galactoside as one of the reaction products. Neither methanol nor ethanol dissociate the subunits of the active tetramer nor do they induce conformational changes in the protein as measured by sedimentation velocity, ultraviolet absorption spectroscopy, and fluorescence. Low concentrations of n-propyl alcohol in the absence of added magnesium ions, however, causes the tetramer to dissociate into inactive dimers. © 1969.