Cassava leaf β-glucosidase specificity and inhibition

Abstract

The specificity of cassava leaf β-glucosidase towards 33 glycosides was examined. Only 11 glycosides were hydrolysed. Among these, there was greater preference for p-nitrophenyl-p-d-glucoside, p-nitrophenyl-β-d-fucoside and linamarin than for o-nitrophenyl-β-d-glucoside, o-nitrophenyl-β-d-fucoside, p-nitrophenyl-β-d-galactoside, p-nitrophenyl-β-d-mannoside, p-nitrophenyl-β-d-xyloside, phenyl-β-glucoside, prunasin and salicin. Glycosides having disaccharide residues as well as α- and β-linked diglucosides were not hydrolysed. The type of glycone and aglycone for the glycoside appeared to be important for enzyme activity. Results of pH dependence studies using p-nitrophenyl-β-d-glucoside, p-nitrophenyl-β-d-fucoside and linamarin as substrates suggested involvement of an acidic amino acid side chain in the enzyme active site. Glucono-1,5-Iactone inhibited the enzyme competitively. The other monosaccharides and their derivatives tested did not show any inhibition of enzyme activity. © 1992.