Effect of aryl substituents on the kinetics of inactivation of glycosidases by glycosylmethylaryltriazenes: examination of the ‘suicide’ nature of these inactivations

The inactivation of the Mg2+-free form of the lacZ-β-galactosidase of Escherichia coli at 25.0 °C by various β-D-galactopyranosylmethylaryltriazenes resembles the spontaneous, rather than the acid-catalysed decomposition of alkylaryltriazenes in that both the maximum first-order rate constant, and the second-order rate constant, are governed by a negative β1g value at pH 7.0 and at pH 8.0. Less extensive data with the β-xylosidase of Penicillium wortmanni and β-D-xylopyranosylmethylaryltriazenes give a similar result. Although the decomposition of the 2-(β-D-galactopyranosyl) ethyl compounds in aqueous solution is 5–10 fold faster than their lower homologues, β-galactosidase inactivation is 3–13 times slower. β-D-Galactopyranosylmethyl-p-nitrophenyltriazene does not inactivate the lectin, RCA ricin.