β-Mannosidase (β-mannoside mannohydrolase, EC 18.104.22.168) was extracted and purified about 100-fold from malted barley. The purified preparation was free of α-mannosidase, β-N-acetylhexosaminidase, α-galactosidase and β-glucosidase. The purified enzyme was active between pH 3 and 6 and exhibited a Km value of 3.2·10-4 M using the p-nitrophenyl-β-d-mannopyranoside as the substrate. 2-Amino-2-deoxy-d-mannose is a competitive inhibitor (K1 = 1.18·10-4 M), p-Nitrophenyl-α-d-mannopyranoside activated the enzyme at low concentration but competitively inhibits at higher concentrations. β-Mannosidase had maximum activity at 55 °C but this dropped significantly at 70 °C. Specific cleavage of β-mannoside linkages by the purified β-mannosidase was demonstrated using a β-(1-4)mannosylmannose as substrate. The enzyme showed the molecular weight is about 88 000 as determined by acrylamide gel electrophoresis.
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