Active-site-directed irreversible inhibition of glycosidases by the corresponding glycosylmethyl-(p-nitrophenyl)triazenes
β-D-Galactopyranosylmethyl-(p-nitrophenyl)triazene is an active-site-directed irreversible inhibitor (ASDIN) of the ebg° and the lacZβ-galactosidases of Escherichia coli, of the β-galactosidase of human-liver lysosomes, and, less effectively, of the α-galactosidase of green coffee beans; it has no effect on the lac repressor of E. coli. β-D-Glucopyranosylmethyl-(p-nitrophenyl)triazene is an ASDIN of both β-glucosidase and β-galactosidase activities of sweet-almond β-glucosidase B; it has no effect on yeast α-glucosidase, the lacZβ-galactosidase of Escherichia coli, or glucoamylase from Aspergillus niger. β-D-Xylopyranosylmethyl-(p-nitrophenyl)triazene is an ASDIN of the β-xylosidase from Penicillium wortmanni, but has no effect on the β-xylosidase of Bacillus pumilus, except by virtue of its consumption of stabilising dithiothreitol. α-L-Arabinofuranosylmethyl-(p-nitrophenyl)triazene is an ASDIN for the extracellular α-L-arabinofuranosidase of Monilinia fructigena of more alkaline pH optimum at pH 7; the other isoenzyme is inert at this pH, and more acidic pHs destroy the reagent. It is concluded that glycosylmethyl(aryl)triazenes are ASDINs for glycosidases for which both substrate and product stereochemistries at the anomeric centre are the same as that of the reagent; that they can act, with lower effectiveness, on glycosidases for which both substrate and product stereochemistries are opposite to that of the reagent; and that they have no effect on glycosidases with opposite stereochemistries of substrate and product, or proteins of no catalytic function.